Disallow post slugs that will result in permalinks that conflict with date archive URLs.

On certain permalink structures, a numeric post slug will result in a post
permalink that conflicts with a date archive URL. For example, with permastruct
`/%year%/%monthnum%/%postname%/`, a post published in May 2015 with slug
`'15'` will result in a URL (`/2015/05/15/`) that conflicts with the archive
for May 15, 2015.

To avoid this problem, `wp_unique_post_slug()` rejects a requested slug when it
would generate a conflict of this type. Thus, in our example, `'15'` would
become `'15-2'`.

Props valendesigns, boonebgorges, Denis-de-Bernardy, loushou.
See #5305.
Built from https://develop.svn.wordpress.org/trunk@32647


git-svn-id: http://core.svn.wordpress.org/trunk@32617 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.3-alpha-32646';
+$wp_version = '4.3-alpha-32647';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.