Merge branch 'zk/push-use-bitmaps'

"git push" sometimes perform poorly when reachability bitmaps are
used, even in a repository where other operations are helped by
bitmaps.  The push.useBitmaps configuration variable is introduced
to allow disabling use of reachability bitmaps only for "git push".

* zk/push-use-bitmaps:
  send-pack.c: add config push.useBitmaps

diff --cc t/t5516-fetch-push.sh
Simple merge