Better is_admin() check from filosofo and pishmishy. fixes #5487 for 2.3

git-svn-id: http://svn.automattic.com/wordpress/branches/2.3@6442 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/admin.php

@@ -1,4 +1,6 @@
 <?php
+define('WP_ADMIN', TRUE);
+
 if ( defined('ABSPATH') )
 	require_once( ABSPATH . 'wp-config.php');
 else

wp-includes/query.php

@@ -32,9 +32,9 @@ function wp_reset_query() {
  */
 
 function is_admin () {
-	global $wp_query;
-
-	return ($wp_query->is_admin || (stripos($_SERVER['REQUEST_URI'], 'wp-admin/') !== false));
+	if ( defined('WP_ADMIN') ) 
+		return WP_ADMIN;
+	return false;
 }
 
 function is_archive () {