Trac Ticket #45 - Fine Grained Password policy:
    if passwordHistory is on, deleting the password fails.
    
    https://fedorahosted.org/389/ticket/45
    
    Bug description: To allow replicating unhashed password, an internal
    entry contains the key value pair when the entry is newly added or
    the password is updated.  In that case, deleting the userpassword
    attribute leaves the unhashed password in the internal entry.
    If you attempt to add a new userpassword, the remaining unhashed
    password makes the attempt fail due to LDAP_TYPE_OR_VALUE_EXISTS.
    
    Fix description: This patch cleans up the unhashed password if a
    userpassword is deleted and the unhashed password is found in the
    internal entry.  If it does not exist, the deletion does nothing.
    (If the entry is read from the database, the unhashed password
    does not exist in the internal entry since it is not stored in
    the database.)