In some unknown way, the one line in Objective-C affects Qt's main
loop causing the crash in QApplication::exec() on processing next
event after that call.
Even crash doesn't happen exactly after this call, it will happen
on application exit. Call stack and disassembly are the same in
all cases.
But running that code in another thread solves the issue.
Created new file src/gui/macutilities.mm, moved code from mainwindow.cpp and torrentcontentmodel.cpp that used the Objective C runtime into it and converted it to actual Objective C. Rewrote pixmapForExtension() so that it doesn't call into private Qt functions.
