astarnode: added GetParent()

astarpath:
added classvars:
vbDebugItems = FALSE (enables/disabled debug apple placement)
viMaxStepCalc = 150 (maximum number of nodes allowed on the closed list before we call the path impossible and resort to old movement)
added properties:
poStartNode and poEndNode to keep track of the start and end objects
plPath to keep track of final path
Removed Debug() messages
Added proper path creation by grabbing each node from poEndNode's parents recursively
removed plHistory listnode recycling