Do not allow current password to be used as new password

Currently when a user changes their password they can enter the same password. In other words if their current password is demo, then they can enter demo as their "new" password. In 1.7.10 we introduce a new feature where administrators can enforce mandatory password changes. This bug creates a loophole around the requirement if users are able to reset their password to the same password.

This check will only be relevant to the current password and the new password that they are entering.