Request: merge change-set from movori branch into master

There is only a theoretical performance advantage to using lis/ori instead of the current lis/addic.
It does clean up the code a little bit as we don't need to deal with adding a negative 16bit value, also the code in MacroAssembler::PatchRelocatedValue() was made less complex for the same reason.
The real value here is that this change-set represents the code that relies on the FIXED_SEQUENCE generated by the mov() code, and is a first step towards two goals:
1) Enabling 64bit mov() implementation
2) Optimizing mov() to output better sequences when a FIXED_SEQUENCE is not required.
All of the code is tagged with FIXED_SEQUENCE to make it easier to find.