replace remnant print by logger.debug to silence synth
pickle tank abstraction
update fuel tanks to sys_actions,

until action_vars arg to synth.synthesize is updated to handle multiple action groups
replace times.clock by os.times

because times.clock does not measure childrens' time, leading to erroneous timings when using multiprocessing. For more details see:

http://linux.die.net/man/2/times