lfs: add the 'lfs' requirement in the changegroup transaction introducing lfs A hook like this is how largefiles manages to do the same. Largefiles uses a changegroup hook, but this uses pretxnchangegroup because that actually causes the transaction to rollback in the unlikely event that writing the requirements out fails. Sadly, the requires file itself isn't rolled back if a subsequent hook fails, but that seems trivial. Now that commit, changegroup and convert are covered, I don't think there's any way to get an lfs repo without the requirement. The grep exit code is blotted out of some test-lfs-serve.t tests now showing the requirement, because run-tests.py doesn't support conditionalizing the exit code.