i965: Work around strangeness in swizzling/masking of gen6 math.

i965: Work around strangeness in swizzling/masking of gen6 math.

Sometimes we swizzled in a different channel it looked like, and
sometimes we swizzled in zero.  Or something.

Having looked at the output of another code generator for this chip,
this is approximately what they do, too: use align1 math on
temporaries, and then move the results into place.

Fixes:
glean/vp1-EX2 test
glean/vp1-EXP test
glean/vp1-LG2 test
glean/vp1-RCP test (reciprocal)
glean/vp1-RSQ test 1 (reciprocal square root)
shaders/glsl-cos
shaders/glsl-sin
shaders/glsl-vs-masked-cos
shaders/vpfp-generic/vp-exp-alias