Avoid lockout when changing the current site domein

[vdboor]

When the current site domein is changed, a developer can lock themselves out of the site. It requires updating the Site and Alias models manually.

Can you add a validator to prevent this from happening?

[jedie]

It's related to #33 isn't it?

[vdboor]

Yes somewhat. #33 is about about a redirect fallback, where as I propose adding a validator to avoid that situation from happening as much as possible.