SH-1682 Use GL_ARB_map_buffer_range to mitigate impact of mapping larger vertex buffer objects.  Limit number of textures per batch to 6 (prevents frame stalls on NVIDIA).

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

* Fixed ATI mac "lighting and shadows" related crash
* Fixed up numerous GL errors on macs related to multiple color formats,
  the use of glEnable/glDisable on textures above the texture unit count
  and old ATI-specific code that was not appropriate for Mac.
* Disabled SSAO for ATI macs due to it not working with shadows
* Ongoing work to properly get shadows and SSAO functioning on ATI macs is required.

Reviewed by davep

Reviewed by Nyx.

fix for VWR-22811: crash at LLImageGL::createGLTexture(int,unsigned char const *,int,int) [secondlife-bin llimagegl.cpp] line 1259

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

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

(transplanted from 72651623d96deee014411daeb82d50452261e0b3)

A proper fix from Richard is coming next.

EXT-6276 Put in some gl flush calls to register combiner functions (why these are being used for UI now is beyond me)

General gl state cleanup in llui.
Make llrender more gGL.begin/end friendly.

I want it to fix glow-through-alpha, but this checkin doesn't includes any of those changes.

I want it to fix glow-through-alpha, but this checkin doesn't includes any of those changes.

I want it to fix glow-through-alpha, but this checkin doesn't includes any of those changes.

Fix for avatar appearance editor drawing hair in the background.

Fix for avatar appearance editor drawing hair in the background.