POSTing DiSCO with ID that matches existing DiSCO causes issues

[karenhanson]

If you copy the rdf for an existing DiSCO and POST it to /discos twice, rather than move the original DiSCO ID to providerId, it will do strange things to the Event record. When you subsequently try to GET that DiSCO, it will complain about having 2 lineageProgenitors. Need to investigate why this doesn't work. Note that when this was observed, the user creating the new DiSCO was different from the user that created the original one.