60% of the way to attacking! Also fixed some minor A* bug. Added
convenience methods to global (accepts point2f instead of 2 floats).

Also made PathfinderMotor a bit cleverer - now it won't pathfind from a
startpoint that is the same as an endpoint, and won't start pathfinding
anew if the endpoint is the same as the last selected endpoint (click
twice rapidly would call the pathfinder twice, silly).