BlobCluster may not properly handle case when two blobs shadow each other in more than one view

[brettviren]

@lastgeorge found the use of setS for edge type in the blob-shadow graph may lead to a problem as it only allows one unique b-b edge for a single view. But, it is possible to have b-b shadows in more than one view.

This line is the hot spot to start looking at this issue:

https://github.com/WireCell/wire-cell-toolkit/blob/master/aux/src/BlobShadow.cxx#L98

[brettviren]

Status update

I believe this is now understood as being due to using setS for edge container.

https://github.com/WireCell/wire-cell-toolkit/blob/master/aux/inc/WireCellAux/BlobShadow.h#L67

@HaiwangYu is working on this in particular replacing setS with multisetS.

A relevant function for accessing edges is boost::edge_range()