Made wfThumbIsStandard() aware of the width/height handler scaling choice

* Generally, either the height or width is used for each description page
  link when using $wgImageLimits. This depends on the $wgImageLimits values
  and the file dimensions. Description page links should better pass the
  wfThumbIsStandard() method now, and thus have weaker rate-limiting.

Change-Id: Id1c3b0fc57f8ed3c14929a1a1661842a069b805d
(cherry picked from commit a530be17cfef51d4e9005082fab29b25616af223)