Merge branch 'jc/autogc'

* jc/autogc:
  git-gc --auto: run "repack -A -d -l" as necessary.
  git-gc --auto: restructure the way "repack" command line is built.
  git-gc --auto: protect ourselves from accumulated cruft
  git-gc --auto: add documentation.
  git-gc --auto: move threshold check to need_to_gc() function.
  repack -A -d: use --keep-unreachable when repacking
  pack-objects --keep-unreachable
  Export matches_pack_name() and fix its return value
  Invoke "git gc --auto" from commit, merge, am and rebase.
  Implement git gc --auto

git-commit.sh

@@ -612,6 +612,7 @@ git rerere
 
 if test "$ret" = 0
 then
+	git gc --auto
 	if test -x "$GIT_DIR"/hooks/post-commit
 	then
 		"$GIT_DIR"/hooks/post-commit