[Piglit] shader_runner churn and framebuffer fetch test generator.

[Francisco Jerez]

The first 17 patches of this series add new functionality to
shader_runner and fix various bugs so EXT_shader_framebuffer_fetch can
get sufficient run-time test coverage by using shader_runner test
scripts alone.  Patch 18 does the actual testing of the framebuffer
fetch extension from a single mako-based generator.  The generator was
originally intended to generate tests for MESA_shader_framebuffer_fetch
and MESA_shader_framebuffer_fetch_non_coherent, but because the
extension text is unfortunately not public yet I've stripped out
everything specific to the MESA extensions for the moment -- If you're
curious about the MESA_shader_framebuffer_fetch tests feel free to
have a look at my piglit repository:

 https://cgit.freedesktop.org/~currojerez/piglit/log/?h=fb-fetch

This depends on the shader_runner parser util rework from this other
series:

 https://lists.freedesktop.org/archives/piglit/2016-October/021061.html

[PATCH 01/18] shader_runner: Don't attempt non-existing GL_TEXTURE_2D enable on GLES2+.
[PATCH 02/18] shader_runner: Rework tracking of texture bindings.
[PATCH 03/18] shader_runner: Take advantage of texture binding book-keeping in image binding command.
[PATCH 04/18] shader_runner: Drop unnecessary texture target argument from fb tex layered command.
[PATCH 05/18] shader_runner: Take advantage of texture binding book-keeping in fb command handling.
[PATCH 06/18] shader_runner: Refactor handling of fb commands.
[PATCH 07/18] shader_runner: Reindent code handling fb commands.
[PATCH 08/18] shader_runner: Allow definition of separate draw and read framebuffers.
[PATCH 09/18] shader_runner: Extend fb tex 2d command to support binding multiple render targets.
[PATCH 10/18] shader_runner: Add fb tex slice binding command.
[PATCH 11/18] shader_runner: Add multisample framebuffer binding command.
[PATCH 12/18] shader_runner: Add winsys framebuffer binding command.
[PATCH 13/18] shader_runner: Add framebuffer blit command.
[PATCH 14/18] shader_runner: Add texture storage command.
[PATCH 15/18] shader_runner: Add blend barrier command.
[PATCH 16/18] shader_runner: Add integer relative probe rect rgba command.
[PATCH 17/18] shader_runner: Fix texture rgbw on GLES.
[PATCH 18/18] Add test generator for EXT_shader_framebuffer_fetch.