EdgeSpec rename should not create extra vertices

[moaxcp]

edge (A, B) {
    renameOne 'C'
}

If A does not already exist this will create three vertices A, B, C. It should only create C and B.

[moaxcp]

I spent a few hours creating a decent solution for this only to realize it breaks the rule that any vertex referenced needs to exist in the graph. It may be ok to fix this for now though.