Batch execution of LastModified query

Summary:
Ref T2683. Further reduces query count of last modified loads; we're now at 11 instead of 200+.

(This works in SVN but could be further optimized.)

Test Plan:
Loaded SVN, Mercurial, Git:

{F34864}
{F34865}
{F34866}

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley, vrana, aran

Maniphest Tasks: T2683

Differential Revision: https://secure.phabricator.com/D5256

src/applications/diffusion/query/DiffusionCommitQuery.php

@@ -250,6 +250,9 @@ final class DiffusionCommitQuery
       $data = mpull($data, null, 'getCommitID');
       foreach ($commits as $commit) {
         $commit_data = idx($data, $commit->getID());
+        if (!$commit_data) {
+          $commit_data = new PhabricatorRepositoryCommitData();
+        }
         $commit->attachCommitData($commit_data);
       }
     }