Disable tests and etc. when destroying framebufs.

Fixes #6678.  May fix problems loading savestates as well.
Disassemble bne/etc. using rs, rt order.

The order makes more logical sense from game disassembly, and matches the
assembler.  Fixes #6632.
Show the replaced instruction in disassembly.

Useful while debugging.
Note the location of a memset variant.
Premultiply for doubled alpha blending if possible.

This makes the effect more accurate where the values were being clamped
before.  Some obscure methods of blending may be slower.
Avoid recalculating replaceBlend so many times.
Avoid premultiplying easy fixed colors.
Dirty the fixed color when premultiplying.
Avoid using fbo copies for the common 2a + 1-2a.

We won't even get it right that often since the copy doesn't deal with
overlap properly.
Improve a possible obscure blend mode.

Seems like this would be likely to get overlap problems.
Optimize fixed color blending that isn't blending.

Gods Eater Burst uses this, for example.
Use correct stencil values with non-add blending.

Otherwise, we get the min/max/etc. value instead.
More correctly blend when hitting the frame cap.

If we hit too many blits per frame, fall back correctly in the shader.