Jit branch debugging

This is like CONDITIONAL_DISABLE for branching.  Off by default.  It's not fast, but not really that slow either.

What it does is:
 * Before the jit compare, flushes and runs the interpreter compare.
 * Records the resulting dest PC, and then continues running jit.
 * After the jit compare, checks the jit dest PC against the interpreter PC.
 * Bails and logs if they don't match (same as a breakpoint.)

Unfortunately (fortunately?), I couldn't find any bad branches in casual browsing, but I think this is pretty useful for debugging.  During this, I also (somewhat related):

 * Added DELAYSLOT and LIKELY flags to the MIPS branch ops.  Needed LIKELY, and DELAYSLOT should improve the cycle estimate.
 * Prevented some stores into ZERO, just to ensure it never varies from 0.

Still haven't found the bug, though...

-[Unknown]