[r6949] conflicts between bridges not checked

[whoami]

With Pak64 r1336: when building bridges (of the same type) in conflict (orthogonal to each other on the same level), i.e. the same way a crossing, this is not prevented, but a crossing is not created either. After that happened, attempts of deleting one bridge may only delete a bridge head each, or otherwise delete the middle parts of a crossing bridge, too. Note: this is what the display says.

[prissi]

This and the other bridges errors are hopefully fixed in r6951.

[whoami]

Yes, it is corrected.