R1:de46a2550c43

Fix auto-close in a repo with missing commits in Phabricator db

Summary:
After adding more error logging: https://secure.phabricator.com/differential/diff/5295/, discover.php prints the output: https://secure.phabricator.com/P427

The problem is that there are gaps in the commits and revisions in Phabricator's DB for the repo. For some git commits, both the phabricator commits and the differential revision are missing (because of a mysterious DB data loss. nharper should be able to recover it); for some…