Keep unhashed password psuedo-attribute in the adding entry
    
    Description:
    unhashed password pseudo-attribute is necessary for plugins that
    handle passwords.  The plugin could be any one including pre/post-
    plugin and be-txn-pre/post-plugin.  On the other hand, the pseudo-
    attribute should not be in the database.
    
    This patch declares the unhashed password pseudo-attribute as an
    operational attribute and allows the pseudo-attribute in an entry
    in the memory.  When creating a flat entry by entry2str_ function
    to store in the database, it omits the pseudo-attribute.
    
    Reviewed by rmeggins@redhat.com and nkinder@redhat.com (Thank you!!)