Merge branch 'ar/run-command-hook-take-2'

Use the hook API to replace ad-hoc invocation of hook scripts via the run_command() API. * ar/run-command-hook-take-2: builtin/receive-pack: avoid spinning no-op sideband async threads receive-pack: convert receive hooks to hook API receive-pack: convert update hooks to new API run-command: poll child input in addition to output hook: add jobs option reference-transaction: use hook API instead of run-command transport: convert pre-push to hook API hook: allow separate std[out|err] streams 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 helper for pp child states t1800: add hook output stream tests