Improve register allocation around moves.
Improve register allocation around moves.

Moves to/from spilled registers will avoid generating excess physical
register move instructions.
Move instructions that occur at the interval boundary for their operands
will try to allocate the destination register in source's physical
register.

froggey/Mezzano,rvedam/Mezzano,froggey/Mezzano,rvedam/Mezzano