Stop errors because of stage counts and null buttons on scene transition.
Fix exponential complexity in CanSupplyResourceRecursive.

The sourceParts list could end up containing multiple instances
of the same part, which causes the recursive walk to misbehave.
Fix both the list and the walk algorithm to avoid this.
Block time between simulations going above 15 seconds.

If something lags the game even at that step, it is a problem
in the simulation that needs to be fixed; without this cutoff
simulations may stall because of random things like swapping.
Show distances of up to 5000km at meter resolution.

The main purpose is precision tuning the SMA of satellite groups.
5000km is just a nice semi-round number higher than the Kerbin-
synchronous orbit.