Fix potential taxon concept representations to facilitate DwC-A creation

[dshorthouse]

There are synonyms with more than one acceptNameUsageID that may indicate taxon concepts rather than taxonomic treatment. eg http://data.canadensys.net/vascan/taxon/9946?lang=en. There is no appropriate way to represent this in DwC unless we create a new taxonID for a second, identically named synonym. The two identical synonyms can then have different acceptedNameUsageIDs. We could also make use of taxonConceptID to bundle the representations so as not to lose sight of what these relationships indicate. However, an auto-generated taxonID is dangerous unless we are certain it will never conflict with future taxonIDs. So, we'd have to prepend these taxonIDs with text or some other flag, which also means they must resolve on VASCAN.

Linked to #8