r300: Redirect constant TEX coordinates

r300: Redirect constant TEX coordinates

R3xx/R5xx fragment program texture constants must come from a hardware
register instead of the constant file, so we redirect if necessary during
the native rewrite phase.

The symptoms of this bug started appearing when the Mesa fixed function
texenvprogram code started using STATE_CURRENT_ATTRIB constants for
texture coordinates when the corresponding attributes were constant across
all vertices.

Signed-off-by: Nicolai Haehnle <nhaehnle@gmail.com>