Allow fragments in link= parameter in <gallery> tags.

This brings the image syntax in gallery tags inline with normal
syntax. Handle <gallery>File:foo.png|link=bar#baz</gallery>
properly.

Bug: 62343
Change-Id: If6149ccc19f70605ad4481e4da2ca55676d6001d
Merge "Allow fragments in link= parameter in <gallery> tags."