Actually logs you in and checks that login was successful.

• Employs protection against a specific IP or user trying to brute force a login to an account.
• On error, uses the same templates Login() uses.
• Checks for various forms of password encryption, allowing you to convert from another system without having to change your password.
• Upgrades password encryption on login, if necessary.
• After successful login, redirects you to $_SESSION['login_url'].
• Accessed from ?action=login2, by forms.