was sooo wrong you wonder how it worked in the first place... Took
me days to find this one!

Also added a new switch, '-o', that lets assign try out solutions
that over-load a pnode. This helps a lot with topologies where the
optimal solution is a best-fit onto multiplexed pnodes.

The end result is that Mike's snake maps much better - it used to get
an essentially random mapping, but now it gets something acceptible.