Index: wp-includes/category-template.php
===================================================================
--- wp-includes/category-template.php	(revision 7599)
+++ wp-includes/category-template.php	(working copy)
@@ -536,4 +536,43 @@
 		echo $return;
 }
 
+/**
+ * has_tag() - Check if the current post has the given tag
+ *
+ * @package WordPress
+ * @since 2.5.1
+ *
+ * @uses wp_get_object_terms() Gets the tags.
+ *
+ * @param string|int|array $tag Optional. The tag name/id/slug or array of them to check for
+ * @return bool True if the current post has the given tag, or any tag, if no tag specified
+ */
+function has_tag($tag = '') {
+       global $post;
+       $taxonomy = 'post_tag';
+
+       if ( !in_the_loop() ) return false; // in-the-loop function
+
+       $post_id = (int) $post->ID;
+
+       $terms = get_object_term_cache($post_id, $taxonomy);
+       if (empty($terms))
+               $terms = wp_get_object_terms($post_id, $taxonomy);
+
+       if (empty($tag)) return (!empty($terms));
+
+       $tag = (array) $tag;
+
+       foreach($terms as $term) {
+               if ( in_array( $term->term_id, $tag ) )
+                       return true;
+               elseif ( in_array( $term->name, $tag ) )
+                       return true;
+               elseif ( in_array( $term->slug, $tag ) )
+                       return true;
+       }
+
+       return false;
+}
+
 ?>