re-implement the forcing hits to be collinear

[rmcolq]

trafficstars

In cluster finding/filtering use collinearity to avoid some spurious hits

[leoisl]

This means requiring hits in a cluster to appear in the same order on a read as on a (single) path through the local graph.

PS: when I read this issue I did not understand anything. I was able to understand it only now, when re-reading your thesis. I am adding this comment for future reference.