Investigate why tst_qobjectrace fails in Symbian

moveToThreadRace case in tst_qobjectrace usually fails in Symbian. The exact cause is unknown, but forcing a context switch by adding printf-call to the end of checkStopWatch function will make the case run properly every time.

The failure manifests as a random panic caused by running out of memory, because the test causes a situation where data->postEventList in QCoreApplicationPrivate never gets cleared while new events are generated en masse into it.

destroyRace case is also failing, though only on emulator, and not always. Armv5 urel will run successfully, but takes long time (about 20 minutes on 5800).