This patch limits the maximum simtime we do simulation computations for.
That is highly sensible if you run flightgear in valgrind or some realy slow
debug build. In such a case it is possible that flightgear gets totally
unresponsible, because simulation time might increase slower than real time.
That patch introduces a maximum simulation time per rendered frame to limit
that effect.
If the property /sim/max-simtime-per-frame is set to something strictly
positive, the simulation time is limited to that value.
The default is unchanged - no limit.
Anyway, from the point of view of gui responsiveness and responsiveness to
realtime controls like joystick inputs it might be a good idea to limit that
by default to say 1 second. If you have less than 1fps, flightgear is
unplayable anyway and I believe we do not longer need to care for realtime
correctness for that case ...