Finally properly fix the flashing on ARM Mali T880 GPU.
The flashing is caused by a 'full pipeline flush' (see DarkPhoton, https://www.opengl.org/discussion_boards/showthread.php/200754-Flashes-on-ARM-Mali?p=1291679&viewfull=1#post1291679 ). In order to combat it, first introduce the possibility that a single DistortedOutputSurface is backed up by more than one FBO. Then make DistortedScreen be derived from DistortedFramebuffer (which itself is derived from DistortedOutputSurface) and make it contain 3 FBOs, render to them in a circular queue fashion, and blit from a given FBO to the system FBO. The 'more than 1 intermediate FBO' queue prevents the pipeline flush....
Port all the 'non-controversial' changes from order-independent-transparency branch.
Disable blending during postprocessing.
Internal API change around postprocessing.
Make Postprocessing quality per-effect (rather than applied to the whole queue)
Minor.
Reorganize the way we add and remove all Effects (do it through DistortedMaster and is POSTPROCES - adjust Bucket and SORT Nodes).
Buggy: removing effects does not work.
Remove old facility to correct Postprocessing buckets on new Postporcessing effects.
New facility will follow shortly....
Remove DistortedEffectsPostprocess and unify it with DistortedEffects.
Job not finished - doesn't compile now!
Progress with support for Effect classes.