Issue #1711938 by Cottser: Fixed 'Last login" block throws errors if there are less than two logins stored for the user.

Issue #1651240 by greggles: avoid WD php: PDOException: SQLSTATE[23000]: Integrity constraint violation: 1048 Column 'user_agent' cannot be null: INSERT INT

Issue #1580798 by greggles | Dave Reid: XSS vulnerability: format_username() needs to be check_plain()'d before output

Issue #1548168 by greggles: log additional data about the login like IP, user agent, and whether or not it was from a one-time login link (and a block)