Index: wp-admin/includes/htaccess.ms
===================================================================
--- wp-admin/includes/htaccess.ms	(revision 12933)
+++ wp-admin/includes/htaccess.ms	(working copy)
@@ -4,7 +4,7 @@
 #uploaded files
 RewriteRule ^(.*/)?files/$ index.php [L]
 RewriteCond %{REQUEST_URI} !.*wp-content/plugins.*
-RewriteRule ^(.*/)?files/(.*) wp-includes/blogs.php?file=$2 [L]
+RewriteRule ^(.*/)?files/(.*) wp-includes/ms-files.php?file=$2 [L]
 
 # add a trailing slash to /wp-admin
 RewriteCond %{REQUEST_URI} ^.*/wp-admin$
Index: wp-includes/blogs.php
===================================================================
--- wp-includes/blogs.php	(revision 12933)
+++ wp-includes/blogs.php	(working copy)
@@ -9,6 +9,135 @@
  */
 
 define( 'SHORTINIT', true );
-require_once( dirname( dirname( __FILE__) ) . '/wp-load.php' ); // absolute includes are faster
-require_once( WP_CONTENT_DIR . '/blogs.php' );
-exit();
+require_once( dirname( dirname( __FILE__ ) ) . '/wp-load.php' );
+ms_default_constants( 'ms-files' );
+
+error_reporting(0);
+
+// Allow wp-content/blogs.php to be used.
+if ( file_exists( WP_CONTENT_DIR . '/blogs.php' ) ) {
+	require_once( WP_CONTENT_DIR . '/blogs.php' );
+	exit;
+}
+
+if ( $current_blog->archived == '1' || $current_blog->spam == '1' || $current_blog->deleted == '1' ) {
+	status_header( 404 );
+	die( '404 — File not found.' );
+}
+
+if ( !function_exists('wp_check_filetype') ) :
+function wp_check_filetype($filename, $mimes = null) {
+	// Accepted MIME types are set here as PCRE unless provided.
+	$mimes = is_array($mimes) ? $mimes : array (
+		'jpg|jpeg|jpe' => 'image/jpeg',
+		'gif' => 'image/gif',
+		'png' => 'image/png',
+		'bmp' => 'image/bmp',
+		'tif|tiff' => 'image/tiff',
+		'ico' => 'image/x-icon',
+		'asf|asx|wax|wmv|wmx' => 'video/asf',
+		'avi' => 'video/avi',
+		'mov|qt' => 'video/quicktime',
+		'mpeg|mpg|mpe' => 'video/mpeg',
+		'txt|c|cc|h' => 'text/plain',
+		'rtx' => 'text/richtext',
+		'css' => 'text/css',
+		'htm|html' => 'text/html',
+		'mp3|mp4' => 'audio/mpeg',
+		'ra|ram' => 'audio/x-realaudio',
+		'wav' => 'audio/wav',
+		'ogg' => 'audio/ogg',
+		'mid|midi' => 'audio/midi',
+		'wma' => 'audio/wma',
+		'rtf' => 'application/rtf',
+		'js' => 'application/javascript',
+		'pdf' => 'application/pdf',
+		'doc' => 'application/msword',
+		'pot|pps|ppt' => 'application/vnd.ms-powerpoint',
+		'wri' => 'application/vnd.ms-write',
+		'xla|xls|xlt|xlw' => 'application/vnd.ms-excel',
+		'mdb' => 'application/vnd.ms-access',
+		'mpp' => 'application/vnd.ms-project',
+		'swf' => 'application/x-shockwave-flash',
+		'class' => 'application/java',
+		'tar' => 'application/x-tar',
+		'zip' => 'application/zip',
+		'gz|gzip' => 'application/x-gzip',
+		'exe' => 'application/x-msdownload'
+	);
+
+	$type = false;
+	$ext = false;
+
+	foreach ( (array) $mimes as $ext_preg => $mime_match ) {
+		$ext_preg = '!\.(' . $ext_preg . ')$!i';
+		if ( preg_match($ext_preg, $filename, $ext_matches) ) {
+			$type = $mime_match;
+			$ext = $ext_matches[1];
+			break;
+		}
+	}
+
+	return compact('ext', 'type');
+}
+endif;
+
+$file = BLOGUPLOADDIR . str_replace( '..', '', $_GET[ 'file' ] );
+if ( !is_file( $file ) ) {
+	status_header( 404 );
+	die( '404 — File not found.' );
+}
+
+$mime = wp_check_filetype( $_SERVER[ 'REQUEST_URI' ] );
+if( false === $mime[ 'type' ] && function_exists( 'mime_content_type' ) )
+	$mime[ 'type' ] = mime_content_type( $file );
+
+if( $mime[ 'type' ] )
+	$mimetype = $mime[ 'type' ];
+else
+	$mimetype = 'image/' . substr( $_SERVER[ 'REQUEST_URI' ], strrpos( $_SERVER[ 'REQUEST_URI' ], '.' ) + 1 );
+
+header( 'Content-type: ' . $mimetype ); // always send this
+if ( false === strpos( $_SERVER['SERVER_SOFTWARE'], 'Microsoft-IIS' ) )
+	header( 'Content-Length: ' . filesize( $file ) );
+
+// Optional support for X-Sendfile and X-Accel-Redirect
+if ( WPMU_ACCEL_REDIRECT ) {
+	header( 'X-Accel-Redirect: ' . str_replace( WP_CONTENT_DIR, '', $file ) );
+	exit;
+} elseif ( WPMU_SENDFILE ) {
+	header( 'X-Sendfile: ' . $file );
+	exit;
+}
+
+$last_modified = gmdate( 'D, d M Y H:i:s', filemtime( $file ) );
+$etag = '"' . md5( $last_modified ) . '"';
+header( "Last-Modified: $last_modified GMT" );
+header( 'ETag: ' . $etag );
+header( 'Expires: ' . gmdate( 'D, d M Y H:i:s', time() + 100000000 ) . ' GMT' );
+
+// Support for Conditional GET
+$client_etag = isset( $_SERVER['HTTP_IF_NONE_MATCH'] ) ? stripslashes( $_SERVER['HTTP_IF_NONE_MATCH'] ) : false;
+
+if( ! isset( $_SERVER['HTTP_IF_MODIFIED_SINCE'] ) )
+	$_SERVER['HTTP_IF_MODIFIED_SINCE'] = false;
+
+$client_last_modified = trim( $_SERVER['HTTP_IF_MODIFIED_SINCE'] );
+// If string is empty, return 0. If not, attempt to parse into a timestamp
+$client_modified_timestamp = $client_last_modified ? strtotime( $client_last_modified ) : 0;
+
+// Make a timestamp for our most recent modification...
+$modified_timestamp = strtotime($last_modified);
+
+if ( ( $client_last_modified && $client_etag )
+	? ( ( $client_modified_timestamp >= $modified_timestamp) && ( $client_etag == $etag ) )
+	: ( ( $client_modified_timestamp >= $modified_timestamp) || ( $client_etag == $etag ) )
+	) {
+	status_header( 304 );
+	exit;
+}
+
+// If we made it this far, just serve the file
+readfile( $file );
+
+?>
Index: wp-includes/ms-default-constants.php
===================================================================
--- wp-includes/ms-default-constants.php	(revision 12933)
+++ wp-includes/ms-default-constants.php	(working copy)
@@ -54,6 +54,20 @@
 			if ( !defined('COOKIE_DOMAIN') )
 					define('COOKIE_DOMAIN', '.' . $current_site->cookie_domain);
 			break;
+		case 'ms-files' :
+			/**
+			 * Optional support for X-Sendfile header
+			 * @since 3.0.0
+			 */
+			if ( !defined( 'WPMU_SENDFILE' ) )
+				define( 'WPMU_SENDFILE', false );
+			/**
+			 * Optional support for X-Accel-Redirect header
+			 * @since 3.0.0
+			 */
+			if ( !defined( 'WPMU_ACCEL_REDIRECT' ) )
+				define( 'WPMU_ACCEL_REDIRECT', false );
+			break;
 	}
 }
 ?>
\ No newline at end of file