Redirect users to upload.wikimedia.org for direct links if okay.

* Currently, users on File: pages are getting unnecessary warnings.
* But if operator supports interstitial-less mdot, this redirects automatically.
* If operator uses interstitial-based mdot, this still prompts.

Change-Id: I3e84a1012ced1a52a91f11278d9f114bb1aa4754
Merge "Redirect users to upload.wikimedia.org for direct links if okay."