Non-active accounts activated on email change confirmation

Previously, when a newly registered user mistyped their password, they would be left unable to activate their account because even after changing their email address to the correct one, they had no way of reaching the account activation email that was sent to the incorrect address. Users would have to contact course ops to have their accounts activated.
To remedy this, account activation and the confirmation of a new email address has been combined for non-active account. The text displayed on the dashboard for newly registered but non-active accounts has also been changed to be less misleading, and to encourage users to check their email addresses and correct them if necessary.
![email-and-account-confirmation-msg](https://cloud.githubusercontent.com/assets/4758600/3650481/abd314f4-111c-11e4-8046-3156a78c78d6.png)

![registration_thanks_msg](https://cloud.githubusercontent.com/assets/4758600/3650486/b51917de-111c-11e4-9cf6-97b67c173303.png)


Did you try ```(not user.is_active)``` and find that it doesn't work in this context?