Avoid database error when `include` or `exclude` is not really a `term_id`. Adds more unit tests.

Props kovshenin.
Fixes #11823.



git-svn-id: https://develop.svn.wordpress.org/trunk@25257 602fd350-edb4-49c9-b593-d223f7449a82
Avoids incorrect results when `url_to_postid()` checking is not strict enough. Adds a bunch of Unit Tests for `url_to_postid()', which is currently only tested lightly in some XML-RPC tests.

Props gcorne, gradyetc.
Fixes #20560.



git-svn-id: https://develop.svn.wordpress.org/trunk@25258 602fd350-edb4-49c9-b593-d223f7449a82