Krunner's spellcheck plugin has been pretty broken since bd291d21f096a714a171e7af3a534ba345ca5659 (about two years ago) because it called Sonnet::Speller::setLanguage every time the spellchecker was invoked, which was (very much) not thread-safe.

This patch makes Sonnet::Speller::setLanguage threadsafe by protecting all access to the internal dict pointer using QReadWriteLock. 

A related review request is 106244, which adds more fixes to the spellcheck feature.

Compiled, installed, used for a week or so, spellchecked a bunch of things.