Making cached glyphs drawing check clearer

Making cached glyphs drawing check clearer

Putting the logic inside supportsTransformation() is a bit confusing and
that name is misleading.

Also move the same check in GL2 paint engine to the same place.

Change-Id: I182500a0ff375122e6be966b7ce2495c84d113d0
Reviewed-on: http://codereview.qt.nokia.com/2096
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@nokia.com>