Pathingdomains

OpenRA island maps are essentially unplayable with the regular AI because the pathfinder always searches out from both the origin and the destination.  If it is trying to route between two different landmasses or bodies of water, this results in a lot of needless searching and consequently intense pathfinding spikes.

I chose the simplest working solution to this that I could think of: this patch assigns a unique integer "domain" to each contiguous mass of land or water, and if a pathfinding request crosses domains, it is invalid and need not be serviced.