Hovercraft behaviour

[Guessmyname]

Can we revert hovercraft behaviour to that of OTA, wherein:

if the hover has upright=1; they do not rotate with terrain
if the hover doesn't have upright=1; they do

as opposed to the current, hardcoded 'do not conform to terrain, even if upright=0; is in the fbi'

I can see why this was done, but some mods (like mine and S44) have amphib tanks that float on the water rather thangoing along the seabed, and when the tanks stop conforming to the terrain, it looks very, very bad.

(NOTE: This is not going to break OTA compatability, as I'm suggesting reverting to the OTA method rather than the hard-codedness of Spring)