Fix weird keycode generator behaviour

[ulissesferreira]

When someone is trying to register with a name that will be converted to a keycode already in use, the API will fail to do so explaining that the email trying to register is already in use. Actually what's happening is that the keycode generator is not smart enough (yet) to detect an already in use keycode and generate another one.

We need this fix because sooner or later there will be people whose keycodes generated from their names will be the same.