Invoke "git gc --auto" from commit, merge, am and rebase.

The point of auto gc is to pack new objects created in loose
format, so a good rule of thumb is where we do update-ref after
creating a new commit.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-am.sh

@@ -466,6 +466,8 @@ do
 		"$GIT_DIR"/hooks/post-applypatch
 	fi
 
+	git gc --auto
+
 	go_next
 done
 

git-commit.sh

@@ -652,6 +652,7 @@ git rerere
 
 if test "$ret" = 0
 then
+	git gc --auto
 	if test -x "$GIT_DIR"/hooks/post-commit
 	then
 		"$GIT_DIR"/hooks/post-commit

git-merge.sh

@@ -82,6 +82,7 @@ finish () {
 			;;
 		*)
 			git update-ref -m "$rlogm" HEAD "$1" "$head" || exit 1
+			git gc --auto
 			;;
 		esac
 		;;

git-rebase--interactive.sh

@@ -307,6 +307,8 @@ do_next () {
 	rm -rf "$DOTEST" &&
 	warn "Successfully rebased and updated $HEADNAME."
 
+	git gc --auto
+
 	exit
 }