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.

kill already-nerfed quadratic attenuation which it seems we won't be supporting any decade soon.

kill already-nerfed quadratic attenuation which it seems we won't be supporting any decade soon.

kill already-nerfed quadratic attenuation which it seems we won't be supporting any decade soon.

cheaply resurrect the difference between spotlight and omnidirectional, as far as the shader is concerned.

not complete.

cheaply resurrect the difference between spotlight and omnidirectional, as far as the shader is concerned.

not complete.

cheaply resurrect the difference between spotlight and omnidirectional, as far as the shader is concerned.

not complete.