Allow p:pipeline in p:library

Did we agree that it's an oversight that p:library is allowed to contain
p:declare-step but not p:pipeline? We did, right?

                                        Be seeing you,
                                          norm

-- 
Norman Walsh <ndw@nwalsh.com> | Where it is permissible both to die and
http://nwalsh.com/            | not to die, it is an abuse of valour to
                              | die.-- Mencius