Merge branch 'nd/daemonize-gc'

Allow running "gc --auto" in the background.

* nd/daemonize-gc:
gc: config option for running --auto in background
daemon: move daemonize() to libgit.a

diff --cc Documentation/config.txt
Simple merge

diff --cc builtin/gc.c
Simple merge

diff --cc cache.h
Simple merge

diff --cc setup.c
Simple merge