[PATCH 0/10] cleaning up check_repository_format_gently

After the discussion in:

  http://thread.gmane.org/gmane.comp.version-control.git/287949/focus=288002

I came up with this series to try to address some of the warts in check_repository_format_gently().

I had hoped to come up with something very small that could go at the front of the refs-backend series, but as with any time I look at the setup code, it managed to snowball into a potpourri of hidden assumptions.

So I hope David isn't _too_ irritated to see this in his inbox. Rebasing the refs-backend on top shouldn't be too bad, and the end result would be cleaner and more correct. My bigger worry is just that changing the setup code is inherently flaky, and I don't want to hold David's series hostage.

  [01/10]: setup: document check_repository_format()
  [02/10]: wrap shared_repository global in get/set accessors
  [03/10]: lazily load core.sharedrepository
  [04/10]: check_repository_format_gently: stop using git_config_early
  [05/10]: config: drop git_config_early
  [06/10]: setup: refactor repo format reading and verification
  [07/10]: init: use setup.c's repo version verification
  [08/10]: setup: unify repository version callbacks
  [09/10]: setup: drop repository_format_version global
  [10/10]: setup: drop GIT_REPO_VERSION constants

-Peff