parse ls-tree with git-submodule correctly

Summary:
git ls-tree gives type 'commit' for submodules.

This code-path is only used when a binary file is present in the diff.

Test Plan: arc diff with a binary file

Reviewers: epriestley

Reviewed By: epriestley

CC: Korvin, aran

Differential Revision: https://secure.phabricator.com/D6943

src/repository/api/ArcanistGitAPI.php

@@ -697,7 +697,7 @@ final class ArcanistGitAPI extends ArcanistRepositoryAPI {
     foreach ($lines as $line) {
       $matches = array();
       $ok = preg_match(
-        '/^(\d{6}) (blob|tree) ([a-z0-9]{40})[\t](.*)$/',
+        '/^(\d{6}) (blob|tree|commit) ([a-z0-9]{40})[\t](.*)$/',
         $line,
         $matches);
       if (!$ok) {