SL-19538 Followup -- scrub all possible sources of NaNs, make dynamic exposure controls not persist, limit exposure range, and do a debug gl pass.

Fix warnings from shaders and include EXTRA_CODE_HERE sentinel in places using DEFINE_GL_FRAGCOLOR for consistency.

Re-added RGB10_A2 normal buffer, this time encoded with a sphere map transform so we can store the environment intensity in the blue channel.

Encode viewspace Z normal to preserve negative Z (fixes all light shifting errors, and shiny environment map errors due to lack of negative Z)

SH-2908 Rework indexed texture rendering to use a uvec4 instead of a float for texture indices in the data stream.  Also rework gl_FragColor overrides to not collide with some odd driver implementations.

SH-2541 Fix for speckles on avatar on some cards -- don't use "maximum_alpha" for alpha tests in shaders as it was always being set to 1.0 anyway.

SH-2243 work in progress -- don't use gl_FragColor or gl_FragData for outputs -- no more deprecation warnings on nvidia

SH-2238, SH-2223, SH-SH-2242 glVertexAttrib throughout main render pipeline complete, preview renders and debug displays still pending.  Also fixed a render glitch and a crash (JIRAs listed).

SH-2181 Fix for alpha flickering when basic shaders enabled (don't use glAlphaFunc when shaders are available).

Reviewed by Leslie