Add more imm handling for shifts in x86 jit.

This is actually hit, and propagates more imms through.
Optimize addi/addiu to just LEA when possible.
Optimize out some addu/etc. calls against imms.
Optimize out slti in the x86 jit.

I'm kinda surprised this actually happens...
Implement ins and ext in the x86 jit.
Add a stub for clz/clo in x86 jit.
Merge pull request #755 from unknownbrackets/jit-minor

More x86 jit stuff