Merge branch 'jc/undecided-is-not-necessarily-sha1-fix'

The base topic started to make it an error for a command to leave
the hash algorithm unspecified, which revealed a few commands that
were not ready for the change.  Give users a knob to revert back to
the "default is sha-1" behaviour as an escape hatch, and start
fixing these breakages.

* jc/undecided-is-not-necessarily-sha1-fix:
  apply: fix uninitialized hash function
  builtin/hash-object: fix uninitialized hash function
  builtin/patch-id: fix uninitialized hash function
  t1517: test commands that are designed to be run outside repository
  setup: add an escape hatch for "no more default hash algorithm" change

diff --cc repository.c
Simple merge