move print_register_file{,_compact} into Registers
separate out HPC counter printing from register file printing

This change is intended to make it easier to verify the subsequent move
of the register printing into Registers.
move register printing for traces into Registers
make compare_register_files return bool

Like the TODO in compare_register_files suggests, none of the callers
care about the particular registers that didn't match up.  So instead of
returning some semi-complicated value, just return true if everything
matches, and false otherwise.
move guts of compare_register_files into Registers
replace most bare register references with their syscall equivalents