NORSPEC-290 Shader optimization WIP -- remove a couple normalizes, pows, and divides from various lighting functions.

NORSPEC-198, NORSPEC-176, NORSPEC-106, NORSPEC-202 et al -- Material matrix testing based overhaul WIP

Reviewed by Graham

NORSPEC-57, NORSPEC-58  Remove sRGB and gamma correction from shaders to remove banding and not break all shiny objects.

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-2507 Potential fix for basic shaders causing objects to disappear with some drivers (prune shader tree of unused shaders while we're at it)

SH-2507 Potential fix for basic shaders causing objects to disappear with some drivers (prune shader tree of unused shaders while we're at it)

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

SH-1682 Dynamically adjust the number of texture channels to use for indexed texture rendering based on available hardware.

See https://wiki.lindenlab.com/wiki/License_Substitution for details.

back-out the back-out for this branch.  yay.

Backing out this merge that I pushed (prematurely) to the wrong place.