Ticket #47384 - Plugin library path validation
    
    Bug description: ldapmodify could replace the plugin path with
    an invalid path.
    
    Fix description: This patch adds the validation code to dse
    callback.  If modify operation is requested for a plugin entry,
    the registered callback check_plugin_path is called and check
    the given plugin path.
    
    This patch also has made get_plugin_name public as slapi_get_
    plugin_name.  Now, the following plugin paths are allowed:
      /path/to/lib<plugin>.so, /path/to/lib<plugin>,
      lib<plugin>.so, lib<plugin>
    
    https://fedorahosted.org/389/ticket/47384
    
    Reviewed by Rich (Thanks!!)