expected behavior when user submits suggested revision identical to existing suggested revision?

[jmcmichael]

Currently we return a 509 if a user submits an entity revision that doesn't contain any edits. In griffithlab/civic-client#88, Obi noted that he was able to submit several identical gene suggested revisions. I had expected that these would genreate 509s as well, but thinking back I don't recall if we discussed/implemented this or not.

As the revisions system is currently implemented, should these identical revisions be generating 509s and did Obi find a bug? Or is returning 509s from identical suggested something we need to discuss and add as an enhancement? (personally I think identical revisions should return a 509 or some other error).