gc --auto: do not lock refs in the background
gc --auto: do not lock refs in the background

9f673f9 (gc: config option for running --auto in background -
2014-02-08) puts "gc --auto" in background to reduce user's wait
time. Part of the garbage collecting is pack-refs and pruning
reflogs. These require locking some refs and may abort other processes
trying to lock the same ref. If gc --auto is fired in the middle of a
script, gc's holding locks in the background could fail the script,
which could never happen before 9f673f9.

Keep running pack-refs and "reflog --prune" in foreground to stop
parallel ref updates. The remaining background operations (repack,
prune and rerere) should not impact running git processes.

Reported-by: Adam Borowski <91edbeada33e2d2ab09eaa593e35685e4ee935c7@angband.pl>
Signed-off-by: Nguyễn Thái Ngọc Duy <024f400cd820cb2ddbe54c7fecfd01e45f30bb96@gmail.com>
Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git