Fixing handling of content node version lookup

Fixes https://www.pivotaltracker.com/story/show/80903880
Why not override `getVersionHistory` on `FedoraBinary`? We should be consistently using our models now (and, if not, should fix them up.).

https://github.com/fcrepo4/fcrepo4/blob/master/fcrepo-kernel-impl/src/main/java/org/fcrepo/kernel/impl/FedoraBinaryImpl.java#L350