[PATCH] Add sign/zero extend to mips fast-isel

[reed kotler]

There are lots of Mips target and ABI variations. The scope of my work at this time is just Mips 32/r2, pic, o32 abi.

Everything else is out of scope.

What is in scope is to finish the whole piece of work for this configuration.

Redoing things that are not part of this scope of work slows down the whole project and is definitely contrary to getting the initial work done.

http://reviews.llvm.org/D4827