Merge branch 'pc/lockfile-pid' into seen

Allow recording process ID of the process that holds the lock next
to a lockfile for diagnosis.

* pc/lockfile-pid:
  lockfile: add PID file for debugging stale locks

builtin/commit.c

@@ -540,7 +540,7 @@ static const char *prepare_index(const char **argv, const char *prefix,
 	path = repo_git_path(the_repository, "next-index-%"PRIuMAX,
 			     (uintmax_t) getpid());
 	hold_lock_file_for_update(&false_lock, path,
-				  LOCK_DIE_ON_ERROR);
+				  LOCK_DIE_ON_ERROR, LOCKFILE_PID_OTHER);
 
 	create_base_index(current_head);
 	add_remove_files(&partial);