Distorted Android

Port a commit from the master branch.

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....

Revert last changes to the postprocessing FBO.

This reverts commit 2dbed690bdbee80d9bfb22c800073855eb5d0946.

Try and avoid re-sorting the children by buckets (if we can!). This makes change in rendering order in the 'Transparency' app actually work.

In an attempt to contain the flashes on Mali GPU, re-structure the post-processing FBOs from 1 FBO with 2 color attachments + combined depth-stencil to 2 separate FBOs sharing a depth-stencil texture.

Result: this appears to make the flashes slightly worse.

Minor

OIT: fixes for Mali: fix a broken loop in the oitRender fragment shader that resulted in flashing.

OIT: fix for 'out of memory' crash on Mali GPUs.

~The thing still does not fully work there - there are still strange flashes in apps that innvolve OIT, for example in 'Triblur'.

OIT: more fixes

OIT: fixes. Everything looks correct now except for the curious return of the 'dancing lower-left corner' small glitch in the 'Transparency' app.

OIT: move towards 4 passes ( clear - build - collapse - render )