Process initial expose events immediately.

Required to prevent qmlscene flicker on startup.

Also brings back that qWait() in tst_QGL::graphicsViewClipping()
that seems necessary after all.

Amended-by: Gabriel de Dietrich <gabriel.dedietrich@digia.com>
Change-Id: I14ba6e18ac98e5df1ce8ecbc263b30176b67d111
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@digia.com>
Reviewed-by: Gunnar Sletta <gunnar.sletta@digia.com>