We are grateful to John Siirola for discussing the design of
multi-task connectors, which strongly influenced the design currently
employed in \code{pyutilib.workflow}.  Sandia National Laboratories
is a multi-program laboratory operated by Sandia Corporation, a
wholly owned subsidiary of Lockheed Martin company, for the U.S.
Department of Energy's National Nuclear Security Administration
under contract DE-AC04-94AL85000.
