QSystemLocale::query() performance issues on OS X (±100 times slower than on Windows)

Test case: https://gist.github.com/707963

This takes about 4 seconds to run on OS X, and only about 40 ms on Windows.

Analysis: http://wimleers.com/blog/qcachinglocale-speeding-up-qsystemlocalequery-calls

Solution: https://github.com/wimleers/QCachingLocale

(Sorry for not rewriting everything nicely here, but that's a lot of duplication, and I think the analysis on my own websites is sufficiently clear and complete to understand the problem. If this annoys anybody, my sincere apologies.)