* (bug 27473) Fix regression: bold, italic no longer interfere with linktrail for...

* (bug 27473) Fix regression: bold, italic no longer interfere with linktrail for ca, kaa

Patch to ca, kaa linktrails to exclude multiple apostrophes by Platonides: https://bugzilla.wikimedia.org/attachment.cgi?id=8337

Added parser test cases to confirm that the linktrail apostrophe works on those languages, and to confirm that the bug where a link is surrounded by bold or italics is resolved.

Tweaked Linker::splitTrail() to keep it from permanently caching $wgContLang's linktrail; when we change content languages during a script run as we do with parser tests, that was leaving us stuck forever on English's linktrail.
This may slightly slow down that path, since it'll have to make a couple brief function calls into the Language object and its data cache.