Merge branch 'rs/child-process-init'

Code clean-up.

* rs/child-process-init:
run-command: inline prepare_run_command_v_opt()
run-command: call run_command_v_opt_cd_env() instead of duplicating it
run-command: introduce child_process_init()
run-command: introduce CHILD_PROCESS_INIT

diff --cc archive-tar.c
Simple merge

diff --cc builtin/commit.c
Simple merge

diff --cc bundle.c
Simple merge

diff --cc daemon.c
Simple merge

diff --cc fetch-pack.c
Simple merge

diff --cc http-backend.c
Simple merge

diff --cc imap-send.c
Simple merge

diff --cc pager.c
Simple merge