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