deprecate cat_is_ancestor_of() in favor of is_cat_ancestor_of()

[ramiy]

change the name "cat_is_ancestor_of()" function to "is_cat_ancestor_of()" like all "is_*()" Conditional tags.

enhancement

the deprecated function belongs in wp-includes/deprecated.php

refreshed patch for 3.0

refreshed patch for 3.0

I'm not convinced here's a need for this. It's not a straight up conditional, it's more complex. We also have a handful of functions we use that are similar, and it's arguably more confusing. We also might be introducing post_is_of_type.

./wp-admin/import/blogger.php:116:	function token_is_valid() {
./wp-admin/includes/image.php:317:function file_is_valid_image($path) {
./wp-admin/includes/image.php:331:function file_is_displayable_image($path) {
./wp-admin/includes/misc.php:635:function win_is_writable($path) {
./wp-includes/category.php:209:function cat_is_ancestor_of( $cat1, $cat2 ) {
./wp-includes/functions.php:2048:function path_is_absolute( $path ) {
./wp-includes/functions.php:3084:function url_is_accessable_via_ssl($url)
./wp-includes/ms-functions.php:1146:function upload_is_user_over_quota( $echo = true ) {
./wp-includes/ms-functions.php:1270:function upload_is_file_too_big( $upload ) {
./wp-includes/post.php:3578:function wp_attachment_is_image( $post_id = 0 ) {
./wp-includes/post.php:4422:function wp_is_post_revision( $post ) {
./wp-includes/post.php:4438:function wp_is_post_autosave( $post ) {