Merge branch 'ar/parallel-hooks'

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()