- issue2550920 - Optionally detect duplicate username at registration. Added config option to allow detection of duplicate username when the user tries to register. Previously user was rejected when dupliate name found at confirmation step. Optional as it can make username guessing easier. Testing is in place for this. Also attempted to make the unfriendly error message: 'node with key "username" exists' into a translatable friendly error: "Username 'username' already exists." This is missing any test. It is also fragile as I capture the ValueError exception and see that the exception matches: 'node with key "username" exists' If it does reassert the friendly message. Otherwise just re-raise existing exception. If the "node with key..." message is translated the friendly override will not trigger.