* Let unprivileged users change their own passwords.

* The password is now an Sconst in the parser, which better reflects its text datatype and also
forces users to quote them.

* If your password is NULL you won't be written to the password file, meaning you can't connect
until you have a password set up (if you use password authentication).

* When you drop a user that owns a database you get an error. The database is not gone.