Mostly, this update provides a select particles in sphere action as part of the new RDF plugin. Part of the reason to do this is to get an easy way to define a selection for an RDF to act on. It makes sense to do it in the RDF plugn so that test scripts for RDF can be guaranteed to have this feature available.
Now, select particles in sphere should really be part of the main application, but to do it right, one should be able to define a sphere object in the same way that you can define a cylinder or plane object. Actually, ellipsoid would be more general. That will be a little extra work, so for now, its just a simple function in the RDF plugin.
