Move objects out of way if they happen to be inside an exclusion area

[Indy2222]

No player is permitted to build anything in a place occupied by units. However due to small delays of pathfinder updates (which is done asynchronously), an object might happen to be inside a static object.

In such a case, the object should move to the closest non-occupied point. If it is moving, new path should be found from the non-occupied point to the target and prepended by the objects current position.

This is related to #98.

[Indy2222]

Due to imprecise object movement, inertia and so on, an object may temporarily or permanently cross exclusion area by some small distance. If a new path is searched during during that moment, none is found and the object gets forever stuck.