Mechjeb Autom8 Enable/Disable AutoControlReleaseWhenStageFuelEmpty()

Purely as an alternate to
http://mumechksp.userecho.com/topic/125055-mechjeb-autom8-vessel-fuel-per-type-per-stage-in-kg-or-l-kgl-and-total/

it would be almost as useful for actual burns if Mechjeb would allow us to specify a setting like Autostage, but when all the fuel in a stage runs out, instead of executing mechjeb.stage(), it executes mechjeb.controlRelease(). This is for long (interplanetary) burns on staged rockets, so we can use mechjeb.busy()/free() to tell when the burn stopped, and then do another mass check to see if we burned as much fuel as we thought. If not, we know we need to call mechjeb.stage(), recalculate the remainder of the burn, and continue on our way.