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

upload-pack.c

@@ -393,7 +393,6 @@ static int get_common_commits(void)
 	char hex[41], last_hex[41];
 	int len;
 
-	track_object_refs = 0;
 	save_commit_buffer = 0;
 
 	for(;;) {