i965: Unalias all GLSL source regs from the destination regs used.

i965: Unalias all GLSL source regs from the destination regs used.

We were doing it ad-hoc before, as instructions with potential
aliasing problems were identified.  But thanks to swizzling basically
anything can have aliasing, so just do it generally at source reg
setup time.  This is somewhat inefficient, because sometimes an
operation doesn't need unaliasing protection if the swizzling is safe,
but the unaliasing before didn't cover those cases either.

Fixes piglit glsl-fs-loop.