Use the hook API to replace ad-hoc invocation of hook scripts via
the run_command() API.
* ar/run-command-hook-take-2:
hook: make ungroup opt-out instead of opt-in
hook: allow hooks to disable stdout_to_stderr
hook: check for NULL pointer before deref
receive-pack: convert receive hooks to hook API
receive-pack: convert update hooks to new API
hooks: allow callers to capture output
run-command: allow capturing of collated output
hook: allow overriding the ungroup option
reference-transaction: use hook API instead of run-command
transport: convert pre-push to hook API
hook: convert 'post-rewrite' hook in sequencer.c to hook API
hook: provide stdin via callback
run-command: add stdin callback for parallelization
run-command: add first helper for pp child states
aef02c57dd