-- Previous algorithms were applying pruneGraph inappropriately on the raw sequence graph (where each vertex is a single base). This results in overpruning of the graph, as prunegraph really relied on the zipping of linear chains (and the sharing of weight this provides) to avoid over-pruning the graph. Probably we should think hard about this. This commit fixes this logic, so we zip the graph between pruning
-- In this process ID's a fundamental problem with how we were trimming away vertices that occur on a path from the reference source to sink. In fact, we were leaving in any vertex that happened to be accessible from source, any vertices in cycles, and any vertex that wasn't the absolute end of a chain going to a sink. The new algorithm fixes all of this, using a BaseGraphIterator that's a general approach to walking the base graph. Other routines that use the same traversal idiom refactored to use this iterator. Added unit tests for all of these capabilities.
-- Created new BaseGraphIterator, which abstracts common access patterns to graph, and use this where appropriate
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