Ref T13280. In D20421, I changed our observe strategy to git fetch <uri> in all cases.

This doesn't work in an ancient, non-bare repository if master is checked out and master is also fetch: git refuses to overwrite the local ref unless we pass --update-head-ok. Pass this flag.

Also, remove some code which examines branches and tags in a special way for non-bare working copies. The old git fetch <origin> code without explicit revsets meant that refs/remotes/orgin/heads/xyz got updated instead of refs/heads/xyz. We now update our local refs in all cases (bare and non-bare) so we can throw away this special casing.

• Replaced a modern bare working copy with a non-bare working copy by explicitly using git clone without --bare.
• Ran bin/repository update, hit the --update-head-ok error. Applied the patch, got a clean update.
• Used the "repository.branchquery" API method...
  • ...with "contains" to trigger the "git branch" case. Got identical results after removing the special casing.
  • ...without "contains" to trigger the "low level ref" case. Got identical results after removing the special casing.
• Grepped for isWorkingCopyBare(). The only remaining callsites deal with hook paths, and genuinely need to be specialized.