More registers

[Leopold Toetsch]

As of rev 7824 Parrot *should* run with NUM_REGISTERS defined as 64 too. 
Only some stack tests are failing that do half frame push and pop tests.

imcc/t/reg/spill_2 just spills 4 registers instead of 36.
Dan, could you please try that with one of your big subroutines and 
report compile times and functionality.

Thanks,
leo