Validation glitch with gateways added from Interfaces > [Name]
If you attempt to add a gateway from Interfaces > WAN and the gateway name already exists, an alert pops up telling the user that the gateway name already exists, but the new gateway is still added to the drop-down list. It is not actually added to the config.xml, however, even if the user presses Save with the new one selected. That part is good, as we don't want to add a duplicate gateway, but it's misleading to the user that it's still in the list before they press Save.
The validation check just needs to either not add, or remove, the new entry from the drop-down if it is rejected.