* Nasal/fuel-and-payload.nas (function trace): new: emit debugging
output whenever the property /b707/fuel/debug is 'true'. Replace all
calls to 'print' with calls to 'trace'.
(array engine_for_tank,
array boost_pump_for-tank,
function boost_pumps_for_tank_are_on): new. Factorize code.
(engines_alive): use them. Change the settimer loop using maketimer.
(crossfeed_control_valves): use them.
(available_receive_capacity_lbs): new, compute how much fuel each tank can receive.
(crossfeed_action): use the above. Change the settimer loop using maketimer.
- Prevent cross-feeding into main 1 and 4 tanks while also transferring from
reserve 1 and 4 tanks, respectively.
- Do not cross-feed more fuel than the receiving tanks can accept.
- Increase the fuel flow from sending tanks to a maximum of 5 pounds/s (the 4 engines
together burn 4.9 pounds/s during cruise, at 2000 kg/h fuel flow). This makes it
possible to cross-feed from the center section to all 4 main tanks during cruise
without starving the engines.
