Use phabricator_ time functions in more places

Summary:
Replace some more date() calls with locale-aware calls.

Also, at least on my system, the DateTimeZone / DateTime stuff didn't actually
work and always rendered in UTC. Fixed that.

Test Plan:
Viewed daemon console, differential revisions, files, and maniphest timestamps
in multiple timezones.

Reviewed By: toulouse
Reviewers: toulouse, fratrik, jungejason, aran, tuomaspelkonen
CC: aran, toulouse
Differential Revision: 530

src/applications/differential/controller/commentpreview/DifferentialCommentPreviewController.php

@@ -42,6 +42,7 @@ class DifferentialCommentPreviewController extends DifferentialController {
     $comment->setAuthorPHID($author_phid);
 
     $view = new DifferentialRevisionCommentView();
+    $view->setUser($request->getUser());
     $view->setComment($comment);
     $view->setHandles($handles);
     $view->setMarkupEngine($engine);