This patch brings url_to_postid into line with the same rewrite rule-matching behavior as that in the parse_request method of WP.
To understand the problem---which has already been fixed in the parse_query method---suppose you have a page with the name blog/comments-preview
Among others, you have the following two rewrite rules:
blog/comments-preview/attachment/([^/]+)/(feed|rdf|rss|rss2|atom)/?$
...
(blog/comments-preview)(/[0-9]+)?/?$
The problem is that ( (! empty($url)) && (strpos($match, $url) === 0) ) returns true on the first rewrite rule, where $match is the rule and $url is blog/comments-preview, so $request_match becomes blog/comments-preview/blog/comments-preview instead of what it should stay as: blog/comments-preview
So when the foreach loop reaches the correctly matching rule, the second one above, it no longer matches, and url_to_postid returns false.
