PAST:Op nodes

PAST::Op nodes represent operations and have the following subtypes:

pirop         # generate a Parrot opcode
call          # call a subroutine
callmethod    # call a method
if            # if ... then ... else
unless        # unless ... then ... else
while         # while ... do ...
until         # until ... do ...
repeat_while  # repeat ... while ...
repeat_until  # repeat ... until ...
try           # try ... catch ... else ...
inline        # inline PIR code
return        # return from a subroutine