SL-18869 Touch up -- Prune "post_pos" from shadow shaders that don't need it and fix non-standard gl_Position z values

SL-18869 Optimizations -- Revive "Frame Profile" and GL_DEPTH_CLAMP.  Remove usage of gl_FragDepth from shadow shaders.

Fix OSX shader compile bug from use of #if FOO instead of #ifdef FOO or #if defined(FOO)
preventing atmospherics (and thus ALM) from working on OSX.

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

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-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-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.

(transplanted from 76dacfb89b155fd1e6698d7affc81fb13ee4fb33)

(transplanted from 76dacfb89b155fd1e6698d7affc81fb13ee4fb33)

Self reviewed.

Merge of QAR-1267 to trunk.  This was a combo merge of QAR-1175 (maint-render-9) and QAR-1236 (dll-msvcrt-2)

svn merge -r 109838:112264 svn+ssh://svn.lindenlab.com/svn/linden/branches/maint-render/maint-render-9-merge-r109833

windlight14 which have passed QA (up through r79932).

svn merge -r 80831:80833 svn+ssh://svn.lindenlab.com/svn/linden/branches/merge_windlight14_r80620