i965/vs: Store texturing results into a vec4 temporary.
i965/vs: Store texturing results into a vec4 temporary.

The sampler appears to ignore writemasks (even when correcting the
WRITEMASK_XYZW in brw_vec4_emit.cpp to the proper writemask) and just
always writes all four values.

To cope with this, just texture into a temporary, then MOV out into a
register that has the proper number of components.

NOTE: This is a candidate for stable branches.

Fixes es3conform's shadow_execution_vert.test.

Signed-off-by: Kenneth Graunke <bd2562f754ec92342f93f61c25d731e290a2ffa8@whitecape.org>
Reviewed-by: Ian Romanick <83437f65a0bd3859f1a0a8228c63010af80a82d4@freedesktop.org>

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