Ignore "Auditors: author" when inferring auditors from commit messages

Summary:
Fixes T12406. When importing commits, we automatically add auditors if the message lists "Auditors: username".

If the list of auditors includes the commit author, this edit fails because you can't audit your own commits (previously, you sometimes could and/or we didn't validate).

Instead, just ignore "Auditors: author".

Test Plan:
  - Made a commit with "Auditors: epriestley".
  - Pushed it.
  - Saw the HeraldWorker get stuck with the error in T12406.
  - Applied the change; worker now succeeded.

Reviewers: chad

Reviewed By: chad

Subscribers: alexmv

Maniphest Tasks: T12406

Differential Revision: https://secure.phabricator.com/D17507

src/applications/audit/editor/PhabricatorAuditEditor.php

@@ -306,6 +306,18 @@ final class PhabricatorAuditEditor
 
     $field_key = DifferentialAuditorsCommitMessageField::FIELDKEY;
     $phids = idx($result, $field_key, null);
+
+    if (!$phids) {
+      return array();
+    }
+
+    // If a commit lists its author as an auditor, just pretend it does not.
+    foreach ($phids as $key => $phid) {
+      if ($phid == $commit->getAuthorPHID()) {
+        unset($phids[$key]);
+      }
+    }
+
     if (!$phids) {
       return array();
     }