Parallelized... but NOT faster!

Well... good news and bad news... I have parallelized the algorithm, and
each of the two threads definitely does meet half of the nodes, but it
takes longer... I'm sure I'm using code that is inefficient... it's much
slower than the serial unidirectional -- I didn't even get a
bidirectional A* to work yet... oh well... that's some kind of
progress!!