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.
git-svn-id: https://develop.svn.wordpress.org/trunk@32647 602fd350-edb4-49c9-b593-d223f7449a82
683ae35c33