Preserve newlines in remarkup previews

Summary: Fixes T10177

Test Plan: Saw that the preview of the rendered task description showed newlines proper.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: Korvin

Maniphest Tasks: T10177

Differential Revision: https://secure.phabricator.com/D15068

src/infrastructure/markup/view/PHUIRemarkupView.php

@@ -24,6 +24,7 @@ final class PHUIRemarkupView extends AphrontView {
 
     return PhabricatorMarkupEngine::renderOneObject(
       id(new PhabricatorMarkupOneOff())
+        ->setPreserveLinebreaks(true)
         ->setContent($corpus),
       'default',
       $viewer);