Ref T13591. Fixes a few issues with the recent updates here discovered in more thorough testing.

• Stopped the daemons.
• Created a new copy of Phabricator in Diffusion.
• Pulled it with bin/repository pull ....
  • Got 17,278 commits on disk with git log --all --format=%H.
• Set permanent refs to "master".
• Discovered it with bin/repository discover ....
  • This took 31.5s and inserted 17,278 tasks.
  • Verified that all tasks have priority 4,000 (PRIORITY_IMPORT).
  • Observed that 16,799 commits have IMPORTED_PERMANENT and 479 commits do not.
    • This matches git log master --format=%H exactly.
• Ran bin/repository refs .... Expected no changes and saw no changes.
• Ran bin/worker execute --active for a minute or two. It processed all the impermanent changes first (since bin/worker is LIFO and these are supposed to process last).
  • Ran bin/repository refs. Expected no changes and saw no changes.
  • Marked all refs as permanent.
  • Starting state: 16,009 message tasks, all at priority 4000.
  • Ran bin/repository refs, expecting 479 new tasks at priority 4000.
  • Saw count rise to 16,488 as expected.
  • Saw all the new tasks have priority 4000 and all commits now have the IMPORTED_PERMANENT flag.