Moved things around in the vectorstore.py class hierarchy again; expanded unit tests a bit more
more work on implementation of get_nearest-neighbors
minor change to conf file for compatiblity with sklearn 0.14;  minor change to the semantics of UnigramVectorSource#get_vector, which now accepts a tuple as well as a string
(BROKEN) started moving to using vectorsource instead of thesaurus, but ran into issues with  migration to sklearn 0.14, needs extra work
(BROKEN) more of the previous, still broken because of incompatibility with sklear 0.14
mostly there