Distorted Android

Minor.

Port the Mali flash fix to the OIT branch.

I am pretty sure this time the flashing issues on Mali T880 r12 driver are finally fixed.

The fix: a queue of FBOs render to, just like before, but this time in DistortedScreen we blit not the current FBO, but the one computed several frames ago.

This of course introduces a delay and uses more memory, but it appears to work and does not seem to have any effects on speed.

Port another commit from master.

I spoke too soon, the ARM Mali flashing is of course not fixed yet. The previous commit fixed Triblur, but the bug is still reproducible elsewhere (only in the 'postprocessed' apps though).

This commit introduces a circular queue in case of the postprocessing FBOs - with little success though.

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.