Reentrant passthrough functions removed, as NamedStreams now fill the same semantic niche, making them redundant.
Added a Parallelisable interface to allow functions to declare whether or not the retain state, or are required to be unique in a parallelised system.  This is included at the level of functions/sources/operations being initialisable, as initialisation = distribution = parallelisation.  This required an update rolled through most of the Function Hierarchy in Squall, as well as the NamedNode hierarchy, the unit tests and elements of the build package.
removed unnecessary imports