add operator< to ConservedPath

So I could sort a list of ConservedPaths it was hopefully going to
let me make simple_refine a little bit better by grouping paths
that were next to each other closer than those that were almost
next to each other execpt one match far away. Unfortunately
I didn't think it all the way through and the lists are already
sorted by that criteria. e.g.

1,1,1 < 1,1,70 < 2,2,2

when what simple refine needis is something more like

1,1,1 < 2,2,2 < 1,1,70