Allow prefilling a task's assignee by his PHID

Summary: Some scripts might find it easier to work with PHIDs instead of user names.

Test Plan:
Use ?assign=<username> and ?assign=<PHID-USER> with the create task URI.
See assignee input being filled correctly.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: epriestley

CC: epriestley, aran, Korvin

Differential Revision: https://secure.phabricator.com/D7401

src/applications/maniphest/controller/ManiphestTaskEditController.php

@@ -100,9 +100,17 @@ final class ManiphestTaskEditController extends ManiphestController {
         if ($can_edit_assign) {
           $assign = $request->getStr('assign');
           if (strlen($assign)) {
-            $assign_user = id(new PhabricatorUser())->loadOneWhere(
-              'username = %s',
-              $assign);
+            $assign_user = id(new PhabricatorPeopleQuery())
+              ->setViewer($user)
+              ->withUsernames(array($assign))
+              ->executeOne();
+            if (!$assign_user) {
+              $assign_user = id(new PhabricatorPeopleQuery())
+                ->setViewer($user)
+                ->withPHIDs(array($assign))
+                ->executeOne();
+            }
+
             if ($assign_user) {
               $task->setOwnerPHID($assign_user->getPHID());
             }