Fix for issue 3698 (Cannot change Directory Manager password with the Control Panel)

The fix consists on using the ldappasswordmodify class to modify the password of the user and to include the current password when the password that is being modified is the one of the user we are bound with.

Using ldappasswordmodify also in the equivalent command-line (which is better than using ldapmodify to modify the password).

The code has also been updated to handle the fact that the password of the user that is being used to configure/manage the OpenDS instance has changed (even after a temporary broken connection to the server, the user will not have to provide it again).