Bug: Trench warfare: using trenches for your advantage

[dmnt]

I encountered this by accident - I seem to be really good in accidental bug discovery.

If you add and remove trenches the terrain graphics tile remains the same but the ground is transformed into clear terrain. A malicious defending player could then generate clear areas in front of his defense positions as much as he likes and force opponent to areas which he thought to be better or create easier routes for operating behind shooting positions.

At least rough and impossible terrain can be transformed this way.