Store the operator table more compactly.

Store the operator table more compactly.

The four cases for each operator:

    none-are-opaque, src-is-opaque, dest-is-opaque, both-are-opaque

are packed into one uint32_t per operator. The relevant strength
reduced operator can then be found by packing the source-is-opaque and
dest-is-opaque into two bits and shifting that number of bytes.

Chris Wilson pointed out a bug in the original version of this commit:
dest_is_opaque and source_is_opaque were used as booleans, but their
actual values were the results of a logical AND with the
FAST_PATH_OPAQUE flag, so the shift value was wildly wrong.

The only reason it actually passed the test suite (on x86) was that
the compiler computed the shift amount in the cl register, and the low
byte of FAST_PATH_OPAQUE happens to be 0, so no shifting actually took
place, and the original operator was returned.