Check for repo+commit when associating review requests with commits.

The post-commit UI had a bug where it would link revisions to review requests
even if the repository didn't match. This wasn't initially found in my testing
since almost all of my testing was with Git (where revisions are SHA-1 hashes),
but does present a problem if there are multiple Subversion repositories (where
revisions are just integers).

Testing done:
Ran unit tests.

Fixes bug 3545.

Reviewed at https://reviews.reviewboard.org/r/6282/