Merge branch 'mk/maint-parse-careful'

* mk/maint-parse-careful:
  receive-pack: use strict mode for unpacking objects
  index-pack: introduce checking mode
  unpack-objects: prevent writing of inconsistent objects
  unpack-object: cache for non written objects
  add common fsck error printing function
  builtin-fsck: move common object checking code to fsck.c
  builtin-fsck: reports missing parent commits
  Remove unused object-ref code
  builtin-fsck: move away from object-refs to fsck_walk
  add generic, type aware object chain walker

Conflicts:

	Makefile
	builtin-fsck.c

builtin-pack-objects.c

@@ -2013,7 +2013,6 @@ static void get_object_list(int ac, const char **av)
 
 	init_revisions(&revs, NULL);
 	save_commit_buffer = 0;
-	track_object_refs = 0;
 	setup_revisions(ac, av, &revs, NULL);
 
 	while (fgets(line, sizeof(line), stdin) != NULL) {