- currently half the shader selection code (GLSL vs ARB) is in
fillGLcaps. The parts that check for software shaders are in
GetDeviceCaps. That placement, will work, but is definitely not optimal.
FillGLcaps should detect support - it should not make decision as to
what's used, because that's not what the purpose of the function is.
GetDeviceCaps should report support as it has already been selected.
Instead, select shader mode in its own function, called in the
appropriate places.

- unifying pixel and vertex shaders into a single selection is a
mistake. A software vertex shader can be coupled with a hardware arb or
glsl pixel shader, or no shader at all. Split them back into two and add
a SHADER_NONE variant.

- drawprim is doing support checks for ARB_PROGRAM, and making shader
decisions based on that - that's wrong, support has already been
checked, and decided upon, and shaders can be implemented via software,
ARB_PROGRAm or GLSL, so that support check isn't valid.

- Store the shader selected mode into the shader itself. Different types
of shaders can be combined, so this is an improvement. In fact, storing
the mode into the settings globally is a mistake as well - it should be
done per device, since different cards have different capabilities.