External login improvements

[Mark]

http://forums.invisionpower.com/index.php?...g_title_id=7976

[bfarber]

To summarize (I hate following links when reading through these), effectively adding another "maintenance url" for the email address would make the login manager more configurable. Right now maintenance url is for both email and password, but PP needs only password changes redirected off site, while letting IPB handle email changes.