A disabled checkbox shows no tooltip, so the settings override that greys
out "ready to go" is now said under it. The consist vehicle count counted
units, so a multi-unit was one vehicle; it now counts cars like the stats bar.
The back of the consist goes to 0 after every change unless its coupler was
set in the editor; a car that gets a neighbour loses that mark, so it is
freed again once it is last again.
The simulator hangs end signals only on a last vehicle with coupler 0; every
new car came with 3 and the pass that couples neighbours never touched the
last one, nor did taking a car off the end. The coupler editor says so for
the last vehicle.
