Support more than 4 texture coordinate registers

[Ivan Gyurdiev]

Ivan Gyurdiev wrote:
> Pixel shaders currently are hardcoded to support 6 tex coordinate 
> registers, only 4 of which have the fragment tex coordinate value 
> copied into them. Patch changes that to make both numbers match 
> min(glMaxTex, numTex), where glMaxTex is the maximum number of texture 
> coordinates supported by OpenGL, and numTex is the maximum number of 
> texture registers supported by the shader version.
>
> This gets rid of many opengl shader errors in LOTR:BFME2, as well as 
> one in HL2.
>
> Applies on top of all the other patches.
>
Please ignore this last patch, I'll implement differently using 
directx.c FillGLCaps().
I am now also a bit confused about how it's supposed to work exactly - 
there's 3 constants involved - MAX_TEXTURE_IMAGE_UNITS_ARB, 
MAX_TEXTURE_COORDS_ARB, and MAX_TEXTURE_UNITS_ARB (where the last one is 
supposed to be "legacy").