[WINED3D] Improve pshader code structure (Try 2: move src handling)

[Ivan Gyurdiev]

Please drop the entire patchset - it introduces a bug, and people have 
various complaints.
I'll work on fixing bugs instead of reorganizing the code.

I think some of this was on the right track, but needs better execution 
(no bugs), and possibly better plan as to how to implement the rest of 
the modifiers and modifier validation.