Index: wp-admin/includes/taxonomy.php
===================================================================
--- wp-admin/includes/taxonomy.php	(revision 14510)
+++ wp-admin/includes/taxonomy.php	(working copy)
@@ -136,7 +136,7 @@
 	if ( $parent < 0 )
 		$parent = 0;
 
-	if ( empty($parent) || !category_exists( $parent ) || ($cat_ID && cat_is_ancestor_of($cat_ID, $parent) ) )
+	if ( empty($parent) || !category_exists( $parent ) || ($cat_ID && is_cat_ancestor_of($cat_ID, $parent) ) )
 		$parent = 0;
 
 	$args = compact('name', 'slug', 'parent', 'description');
Index: wp-includes/category.php
===================================================================
--- wp-includes/category.php	(revision 14510)
+++ wp-includes/category.php	(working copy)
@@ -200,13 +200,13 @@
  * You can use either an id or the category object for both parameters. If you
  * use an integer the category will be retrieved.
  *
- * @since 2.1.0
+ * @since 3.0
  *
  * @param int|object $cat1 ID or object to check if this is the parent category.
  * @param int|object $cat2 The child category.
  * @return bool Whether $cat2 is child of $cat1
  */
-function cat_is_ancestor_of( $cat1, $cat2 ) {
+function is_cat_ancestor_of( $cat1, $cat2 ) {
 	if ( ! isset($cat1->term_id) )
 		$cat1 = &get_category( $cat1 );
 	if ( ! isset($cat2->parent) )
@@ -217,7 +217,7 @@
 	if ( $cat2->parent == $cat1->term_id )
 		return true;
 
-	return cat_is_ancestor_of( $cat1, get_category( $cat2->parent ) );
+	return is_cat_ancestor_of( $cat1, get_category( $cat2->parent ) );
 }
 
 
Index: wp-includes/deprecated.php
===================================================================
--- wp-includes/deprecated.php	(revision 14510)
+++ wp-includes/deprecated.php	(working copy)
@@ -2513,3 +2513,22 @@
 	_deprecated_function( __FUNCTION__, '3.0' );
 	return '';
 }
+
+/**
+ * Check if a category is an ancestor of another category.
+ *
+ * @since 2.1.0
+ * @deprecated 3.0
+ * @deprecated Use is_cat_ancestor_of()
+ * @see is_cat_ancestor_of()
+ *
+ * @param int|object $cat1 ID or object to check if this is the parent category.
+ * @param int|object $cat2 The child category.
+ * @return bool Whether $cat2 is child of $cat1
+ */
+function cat_is_ancestor_of( $cat1, $cat2 ) {
+	_deprecated_function( __FUNCTION__, '3.0', 'is_cat_ancestor_of()' );
+
+	return is_cat_ancestor_of( $cat1, $cat2 );
+}
+