When a commit appears as an ancestor of a permanent ref for the first time, run all import steps

Summary:
Depends on D20427. Ref T13277. As an optimization, when we discover that a commit which was previously only on a non-permanent ref ("tmp-epriestley-123") is now reachable from a permanent ref ("master"), we currently queue only a new "message" parse step.

This is an optimization because these commits previously got the full treatment (feed, publish, audit, etc) as soon as they were discovered. Now, those steps only happen once a commit is reachable from a permanent ref, so we need to run everything.

Test Plan:

• Pushed local "tmp-123" branch to remote tag "tmp-123".
• Updated repository with "bin/repository update", saw commit import as a "not on any permanent ref" commit, with no herald/audit/etc.
• Merged "tmp-123" tag into "master".
• Pushed new "master".
• Updated repository with "bin/repository refs ... --trace --verbose", saw commit detected as now reachable from a permament ref.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13277

Differential Revision: https://secure.phabricator.com/D20428