Bug 54745: Link.langlinkUnsafe interwiki_forward

- Site.pagelanglinks (and others) use Link.langlinkUnsafe,
  which didnt respect Family.interwiki_forward. This caused
  interwiki links on Commons to link to Commons pages.

Change-Id: Ia30b7b7dd2b4349a72e0594f135695848cf61bdb
Merge "Bug 54745: Link.langlinkUnsafe interwiki_forward"