|  Respuesta: ¿Como descargar archivo solo una vez?  
  Bueno si,lo que pasa es que solo puse la parte a agregar dentro del archivo php,todo el archivo en si contiene esto:
 
 <?php
 
 //Permite que solo Googlebot tenga acceso a areas restringidas;
 
 
 <span onmouseover="_tipon(this)" onmouseout="_tipoff()"> </span> <span class="google-src-text" style="direction: ltr; text-align: left"> </span>
 $allow_inside = ($ is_logged_in) || substr_count($ _SERVER  ['HTTP_USER_AGENT'],'Googlebot');
 $allow_inside = ($ is_logged_in) || substr_count($ _SERVER ['HTTP_USER_AGENT'],'Googlebot');
 
 
 // Set flag that this is a parent file
 define( '_VALID_MOS', 1 );
 
 // checks for configuration file, if none found loads installation page
 if (!file_exists( 'configuration.php' ) || filesize( 'configuration.php' ) < 10) {
 $self = rtrim( dirname( $_SERVER['PHP_SELF'] ), '/\\' ) . '/';
 header("Location: http://" . $_SERVER['HTTP_HOST'] . $self . "installation/index.php" );
 exit();
 }
 
 require( 'globals.php' );
 require( 'configuration.php' );
 
 // SSL check - $http_host returns <live site url>:<port number if it is 443>
 $http_host = explode(':', $_SERVER['HTTP_HOST'] );
 if( (!empty( $_SERVER['HTTPS'] ) && strtolower( $_SERVER['HTTPS'] ) != 'off' || isset( $http_host[1] ) && $http_host[1] == 443) && substr( $mosConfig_live_site, 0, 8 ) != 'https://' ) {
 $mosConfig_live_site = 'https://'.substr( $mosConfig_live_site, 7 );
 }
 
 require_once( 'includes/joomla.php' );
 
 //Installation sub folder check, removed for work with SVN
 if (file_exists( 'installation/index.php' ) && $_VERSION->SVN == 0) {
 define( '_INSTALL_CHECK', 1 );
 include ( $mosConfig_absolute_path .'/offline.php');
 exit();
 }
 
 // displays offline/maintanance page or bar
 if ($mosConfig_offline == 1) {
 require( $mosConfig_absolute_path .'/offline.php' );
 }
 
 // load system bot group
 $_MAMBOTS->loadBotGroup( 'system' );
 
 // trigger the onStart events
 $_MAMBOTS->trigger( 'onStart' );
 
 if (file_exists( $mosConfig_absolute_path .'/components/com_sef/sef.php' )) {
 require_once( $mosConfig_absolute_path .'/components/com_sef/sef.php' );
 } else {
 require_once( $mosConfig_absolute_path .'/includes/sef.php' );
 }
 require_once( $mosConfig_absolute_path .'/includes/frontend.php' );
 
 // retrieve some expected url (or form) arguments
 $option = strval( strtolower( mosGetParam( $_REQUEST, 'option' ) ) );
 $Itemid = intval( mosGetParam( $_REQUEST, 'Itemid', null ) );
 
 if ($option == '') {
 if ($Itemid) {
 $query = "SELECT id, link"
 . "\n FROM #__menu"
 . "\n WHERE menutype = 'mainmenu'"
 . "\n AND id = " . (int) $Itemid
 . "\n AND published = 1"
 ;
 $database->setQuery( $query );
 } else {
 $query = "SELECT id, link"
 . "\n FROM #__menu"
 . "\n WHERE menutype = 'mainmenu'"
 . "\n AND published = 1"
 . "\n ORDER BY parent, ordering"
 ;
 $database->setQuery( $query, 0, 1 );
 }
 $menu = new mosMenu( $database );
 if ($database->loadObject( $menu )) {
 $Itemid = $menu->id;
 }
 $link = $menu->link;
 if (($pos = strpos( $link, '?' )) !== false) {
 $link = substr( $link, $pos+1 ). '&Itemid='.$Itemid;
 }
 parse_str( $link, $temp );
 /** this is a patch, need to rework when globals are handled better */
 foreach ($temp as $k=>$v) {
 $GLOBALS[$k] = $v;
 $_REQUEST[$k] = $v;
 if ($k == 'option') {
 $option = $v;
 }
 }
 }
 if ( !$Itemid ) {
 // when no Itemid give a default value
 $Itemid = 99999999;
 }
 
 // mainframe is an API workhorse, lots of 'core' interaction routines
 $mainframe = new mosMainFrame( $database, $option, '.' );
 $mainframe->initSession();
 
 // trigger the onAfterStart events
 $_MAMBOTS->trigger( 'onAfterStart' );
 
 // checking if we can find the Itemid thru the content
 if ( $option == 'com_content' && $Itemid === 0 ) {
 $id 	= intval( mosGetParam( $_REQUEST, 'id', 0 ) );
 $Itemid = $mainframe->getItemid( $id );
 }
 
 /** do we have a valid Itemid yet?? */
 if ( $Itemid === 0 ) {
 /** Nope, just use the homepage then. */
 $query = "SELECT id"
 . "\n FROM #__menu"
 . "\n WHERE menutype = 'mainmenu'"
 . "\n AND published = 1"
 . "\n ORDER BY parent, ordering"
 ;
 $database->setQuery( $query, 0, 1 );
 $Itemid = $database->loadResult();
 }
 
 // patch to lessen the impact on templates
 if ($option == 'search') {
 $option = 'com_search';
 }
 
 // loads english language file by default
 if ($mosConfig_lang=='') {
 $mosConfig_lang = 'english';
 }
 include_once( $mosConfig_absolute_path .'/language/' . $mosConfig_lang . '.php' );
 
 // frontend login & logout controls
 $return 	= strval( mosGetParam( $_REQUEST, 'return', NULL ) );
 $message 	= intval( mosGetParam( $_POST, 'message', 0 ) );
 
 // Get the information about the current user from the sessions table
 $my = $mainframe->getUser();
 
 if ($option == 'login') {
 $mainframe->login();
 
 // JS Popup message
 if ( $message ) {
 ?>
 <script language="javascript" type="text/javascript">
 <!--//
 alert( "<?php echo addslashes( _LOGIN_SUCCESS ); ?>" );
 //-->
 </script>
 <?php
 }
 
 if ( $return && !( strpos( $return, 'com_registration' ) || strpos( $return, 'com_login' ) ) ) {
 // checks for the presence of a return url
 // and ensures that this url is not the registration or login pages
 // If a sessioncookie exists, redirect to the given page. Otherwise, take an extra round for a cookiecheck
 if (isset( $_COOKIE[mosMainFrame::sessionCookieName()] )) {
 mosRedirect( $return );
 } else {
 mosRedirect( $mosConfig_live_site .'/index.php?option=cookiecheck&return=' . urlencode( $return ) );
 }
 } else {
 // If a sessioncookie exists, redirect to the start page. Otherwise, take an extra round for a cookiecheck
 if (isset( $_COOKIE[mosMainFrame::sessionCookieName()] )) {
 mosRedirect( $mosConfig_live_site .'/index.php' );
 } else {
 mosRedirect( $mosConfig_live_site .'/index.php?option=cookiecheck&return=' . urlencode( $mosConfig_live_site .'/index.php' ) );
 }
 }
 
 } else if ($option == 'logout') {
 $mainframe->logout();
 
 // JS Popup message
 if ( $message ) {
 ?>
 <script language="javascript" type="text/javascript">
 <!--//
 alert( "<?php echo addslashes( _LOGOUT_SUCCESS ); ?>" );
 //-->
 </script>
 <?php
 }
 
 if ( $return && !( strpos( $return, 'com_registration' ) || strpos( $return, 'com_login' ) ) ) {
 // checks for the presence of a return url
 // and ensures that this url is not the registration or logout pages
 mosRedirect( $return );
 } else {
 mosRedirect( $mosConfig_live_site.'/index.php' );
 }
 } else if ($option == 'cookiecheck') {
 // No cookie was set upon login. If it is set now, redirect to the given page. Otherwise, show error message.
 if (isset( $_COOKIE[mosMainFrame::sessionCookieName()] )) {
 mosRedirect( $return );
 } else {
 mosErrorAlert( _ALERT_ENABLED );
 }
 }
 
 // detect first visit
 $mainframe->detect();
 
 // set for overlib check
 $mainframe->set( 'loadOverlib', false );
 
 $gid = intval( $my->gid );
 
 // gets template for page
 $cur_template = $mainframe->getTemplate();
 /** temp fix - this feature is currently disabled */
 
 /** @global A places to store information from processing of the component */
 $_MOS_OPTION = array();
 
 // precapture the output of the component
 require_once( $mosConfig_absolute_path . '/editor/editor.php' );
 
 ob_start();
 
 if ($path = $mainframe->getPath( 'front' )) {
 $task 	= strval( mosGetParam( $_REQUEST, 'task', '' ) );
 $ret 	= mosMenuCheck( $Itemid, $option, $task, $gid );
 
 if ($ret) {
 require_once( $path );
 } else {
 mosNotAuth();
 }
 } else {
 header( 'HTTP/1.0 404 Not Found' );
 echo _NOT_EXIST;
 }
 
 $_MOS_OPTION['buffer'] = ob_get_contents();
 
 ob_end_clean();
 
 initGzip();
 
 header( 'Expires: Mon, 26 Jul 1997 05:00:00 GMT' );
 header( 'Last-Modified: ' . gmdate( 'D, d M Y H:i:s' ) . ' GMT' );
 header( 'Cache-Control: no-store, no-cache, must-revalidate' );
 header( 'Cache-Control: post-check=0, pre-check=0', false );
 header( 'Pragma: no-cache' );
 
 // display the offline alert if an admin is logged in
 if (defined( '_ADMIN_OFFLINE' )) {
 include( $mosConfig_absolute_path .'/offlinebar.php' );
 }
 
 // loads template file
 if ( !file_exists( $mosConfig_absolute_path .'/templates/'. $cur_template .'/index.php' ) ) {
 echo _TEMPLATE_WARN . $cur_template;
 } else {
 require_once( $mosConfig_absolute_path .'/templates/'. $cur_template .'/index.php' );
 echo '<!-- '. time() .' -->';
 }
 
 // displays queries performed for page
 if ($mosConfig_debug) {
 echo $database->_ticker . ' queries executed';
 echo '<pre>';
 foreach ($database->_log as $k=>$sql) {
 echo $k+1 . "\n" . $sql . '<hr />';
 }
 echo '</pre>';
 }
 
 doGzip();
 ?>
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