Allow simulation of auto-repeat key events in qtestlib

Currently it's not possible to use QTestLib to test for auto-repeat key events (i.e. when holding down a key).

Perhaps QTest::keyPress(), QTest::keyRelease() and QTest::keyClick() could accept a 'repeat' argument. It looks like the undocumented QTest::simulateEvent() accepts this as an argument already, but QTest::sendKeyEvent() hard-codes the repeat value before passing it to simulateEvent().