The rewritten threaded render loop causes crashes on close

The following change in qtdeclarative seems to cause crash-on-exit problems for the desktop components (possibly only on Mac OSX).

commit ebe8b9408cfcd953fae80514aa67e49221541bed
Author: Gunnar Sletta <gunnar.sletta@digia.com>

Complete rewrite of threaded render loop.

Just run the gallery example (qmlscene examples/gallery/main.qml) and close it. On close, it will often output such warnings as "QOpenGLContext::swapBuffers() called with non-exposed window, behavior is undefined" and eventually crash. I have attached a couple of backtraces, both crashes in QSGRenderThread.