Regular skies need it off but SkyViewpoints need it on - and all others need to use the parent's setting.
So without engine side tracking we can end up rendering the sky with this setting off, resulting in omission of the fog layer.
- use sampler objects to avoid creating up to 4 different system textures for one game texture just because of different clamping settings.
- avoids flushing all textures for change of texture filter mode.
- separate sprite and regular dimensions on the material level to have better control over which one gets used. It's now an explicit parameter of ValidateTexture. The main reason for this change is better handling of wall sprites which may not be subjected to such handling.
- create mipmaps based on use case, not texture type.
- allows removal of FCloneTexture hack for proper sharing of the same sprite for decals and other purposes.
- better precaching of skyboxes.
- reactivate alpha testing per fixed function pipeline
- use the 'modern' way to define clip planes (GL_CLIP_DISTANCE). This is far more portable than the old glClipPlane method and a lot more robust than checking this in the fragment shader.
- removed gl_vid_compatibility. With the bump to 1.4 no hardware requiring this flag is supported anymore.
- disabled 16 bit framebuffers for the same reason. As a conseqence all code for rendering without stencil could also be removed.
