Hook scripts defined via the configuration system can now be
configured to run in parallel.
* ar/parallel-hooks:
t1800: test SIGPIPE with parallel hooks
hook: allow hook.jobs=-1 to use all available CPU cores
hook: add hook.<event>.enabled switch
hook: move is_known_hook() to hook.c for wider use
hook: warn when hook.<friendly-name>.jobs is set
hook: add per-event jobs config
hook: add -j/--jobs option to git hook run
hook: mark non-parallelizable hooks
hook: allow pre-push parallel execution
hook: allow parallel hook execution
hook: parse the hook.jobs config
config: add a repo_config_get_uint() helper
repository: fix repo_init() memleak due to missing _clear()
718db095c2