-- Cosmetic changes in register allocator.

-- Implement macro HP_GEN_SEQ_NP.

-- MachCode(trivialCode, x86): because one of the operands is also
   the destination (on this 2-address arch), it's invalid to sequence
   the code to compute the operands using asmParThen [code1, code2].
   since the order of assignments matters.  Fixed.