Add compat code for 'image' post format.

see #19570. props wonderboymusic.

git-svn-id: http://core.svn.wordpress.org/trunk@23847 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/js/post-formats.js

@@ -118,7 +118,7 @@ window.wp = window.wp || {};
 				mediaPreview('video', url, mime);
 			} else {
 				// set the hidden input's value
-				$field.val(url);
+				$field.val(id);
 				// Show the image in the placeholder
 				$el.html('<img src="' + url + '" />');
 				$holder.removeClass('empty').show();