In `get_adjacent_post()`, `$excluded_terms` should check term_id rather than term_taxonom_id.

See #29663, #22112.

git-svn-id: https://develop.svn.wordpress.org/trunk@30263 602fd350-edb4-49c9-b593-d223f7449a82
Add tests for `get_adjacent_post_link()` wrappers.

Props MikeHansenMe.
See #29663.

git-svn-id: https://develop.svn.wordpress.org/trunk@30264 602fd350-edb4-49c9-b593-d223f7449a82