Use SSE2 in debug and x64, not just x86.

Apples to apples is nice.  More accurate floats in debug is bad.
Disasm transposed vectors properly.
Fix jit VDot mapping vd incorrectly to a quad.
Respect the writemask in VDot.

Although it's basically a no-op in that case...
Add a flag for eating prefixes to the MIPS tables.

Still incomplete, just filled in ones I've tested so far.
Automatically eat prefixes in x86 jit.

Simplifies the code and makes it easier to know they're eaten
even for ops not yet jitted.
Re-enable vdot and vadd/etc. in x86 jit.
Mark more instructions that eat prefixes.
Merge pull request #728 from unknownbrackets/jit-vfpu

Fix and re-enable vdot again on x86