SET&QUERY - party.c

set_leader(o): This notifies the party object that the leader object is object
               o.
               Example: party->set_leader(this_object());
set_nr(i): This sets the member number of this partyitem to i. The member
           number needs to be unique in one party.
           Example: party->set_nr(5);
query_leader(): This returns the object of the leader.
query_nr(): This returns the member number of this party object.
