Load password information when expiring

Call loadPasswords when expiring the user's password, otherwise the
change is overwritten with the previous value.

This lets you do:
  $u = User::newFromName( 'User' );
  $u->expirePassword();
And the user will have to reset their password on the next login.

Change-Id: I47325dde1ce14280088efdc90ce7887b45e0dc6a
Merge "Load password information when expiring"