R1:9d8b5481aec5

Emit full URIs to identify Differential revisions

Summary:
- Previously, used IDs like "33" to match a commit to a Differential revision.
This has a namespacing problem because we now have an arbitrarily large number
of Phabricator installs in the world, and they may want to track commits from
other installs.
- In Differential, parse raw IDs or full URIs. Emit only full URIs.
- In Repositories, parse only full URIs.
- This might cause a few commits to not be picked up in rare circumstances.
Users…