Respect Content-Type encoding in HTTP response status

Test Plan:
  $future = new HTTPSFuture('http://jakub.vrana.cz/');
  list($status) = $future->resolve();
  echo $status->getMessage() . "\n";

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D6428