- unify per-version cases into a single sequence
- make use of get_register_name() for the destination register
- ignore destination write mask - it's only allowed on 2.0+ shaders,
  and only the default mask is allowed there (xyzw)
- enable swizzle on texld 1.4 (it works together with dw/dz modifiers)
- implement for shaders 2.0-3.0

- add missing GL type and make GL cfg entries for A16B16G16R16
- correct L16 type to UNSIGNED_SHORT (..16 = short, not byte)
- change internal format for X8R8G8B8 from GL_RGB to GL_RGB8 which
  seems more correct

Based on a patch by qingdoa daoo.