Space around summoned items

Changes in cvs so that before an engineer spawns something it checks there will still be space to get by it.

In short, this means:

You will not be able to put that last block at the top of a wall to block it up to the ceiling. However, you will be able to horizontally fill the corridor.

Sentinels can still be spawned in corridors, provided the corridor is not too small.

Vehicles and turrets need a bigger space in which to spawn. This is unlikely to be in a corridor. It could be in a room provided it does not have a low ceiling

Hopefully, this will go some way to stopping corridors being blocked by Engineers.

kick butt!