Fixed #2086 -- Changed `base.css` to import `null.css` (added in [6197]) instead of `null`.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@6716 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/contrib/admin/media/css/base.css

@@ -4,11 +4,11 @@
 */
 
 /* Block IE 5 */
-@import "null?\"\{";
+@import "null.css?\"\{";
 
 /* Import other styles */
 @import url('global.css');
 @import url('layout.css');
 
 /* Import patch for IE 6 Windows */
-/*\*/ @import "patch-iewin.css"; /**/
\ No newline at end of file
+/*\*/ @import "patch-iewin.css"; /**/