qt: fix broken unicode chars on osx 10.10

The default font changed again.

The real fix is to compile qt against a >= 10.8 sdk, but this is simple enough
to backport to 0.10 to avoid having to do that there.

Note: NSAppKitVersionNumber is a double and there's no official value for
NSAppKitVersionNumber10_10. Since == isn't reliable for doubles, use Apple's
guidelines for testing versions here:
https://developer.apple.com/library/mac/releasenotes/AppKit/RN-AppKit/

Chinese and Japanese fonts have been hard-coded as well, otherwise they fail to
show up at all.