Make QQuickWindow::forcePolish() private.

Adding public API was not the intention when adding
this slot.

Change-Id: If477917c434b32d5e5cd1fa6c640f1a6b167dd24
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>
Workaround for glyph upload bug with the Mali-400 GPU.

Uploading unaligned and alpha-only data seems to be broken with that
GPU, uploading line by line does the trick.

Task-number: QTBUG-33951
Change-Id: I2790990ca1d3a3016ec3d9fefaea7002b92faeb7
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@digia.com>
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>