(bug 27111) Make cascading foreign repo's fetch description properly

(bug 27111) Make cascading foreign repo's fetch description properly

This changes action=render on file pages to include the shared image
description (if it exists). The reasons for this are two fold:

*Logically, most users would consider the shared description part of
  the content of the page, and not part of the site chrome, so it
  should be on action=render
*Foreign file repos use action=render to get image descriptions.
  if you use say en.wikipedia.org as your file repo, commons images
  get cascasively included, but all their descriptions end up
  being the noarticletext message, which is bad. This makes
  the shared image descriptions work.

Some notes on the implementation:
* on action=render the div containing the shared description
  doesn't have the id that the one on normal page view has.
  This is to prevent duplicate ids in the cascading repo scenario.
  I added a class so people can identify them if they want, and this
  allows people to easily identify the "outermost" shared description
  as it would be the only one with the id.
* This doesn't include the "shareddescriptionfollows" message
  (which is disabled by default) that would normally separate the
  local from the non-local description. I wasn't sure, but thought
  that would be considered part of the site chrome.

Patchset 2/3: trailing space/spelling mistake
Patchset 4: rebase

Change-Id: I18bdf29de62526d699740607b5015da4b01fd43d