Enforce texture cleanup to happen at the end of the sync phase.

This was ok for the threaded renderer, but for the single-threaded
renderers where the event loop was spinning we could run the risk
of scheduling a texture for deleteLater() and then cleaning it
up before we got around to the sync phase.

Task-number: QTBUG-35670
Change-Id: I92074294b427fd8ab2a1823ba79c7ac3b59094ec
Reviewed-by: Michael Brasser <michael.brasser@live.com>
Only look at alpha to decide if rectangle has fill or not.

Task-number: QTBUG-35606
Change-Id: Id403047e19e75d91ec3b3f8367166d8ec96ecaf8
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>