Add post-login redirect to originally requested URL

[ZimbiX]

When I'm not logged in and click a 'Mark as Purchased' link from my email, after I log in, the album doesn't get marked as purchased; whereas if I am already logged in, it does.

To fix this, the login page should redirect back to the requested URL post-login.

[pat]

Sounds reasonable to me. Don't suppose you've got the time to sort out a PR? :)