CenterStage Object Class:  DataFromGroup
Subclass of:  Polyhedron
Requires a reference to a Group object

The DataFromGroup class provides a means of using the data already computed
by another Group object.  One reason to do this is to make a
ShowMe checkbox that can be used to turn the group on and off without
recomputing it (or any other objects linked to it).  To do this, make a
Group object that has its OBJECT/SHOW menu set to NEVER, and then create a
DataFromGroup object that links to it and has the CheckBox and ShowMe
directives.  When the DataFromGroup object is first shown, it will force
the Group object to compute the data, and then the DataFromGroup object
will be able to use that data whenever it is shown, without recomputing it.

Unlike the other DataFrom... classes, the DataFromGroup object converts all 
the data from Surface and Curve objects to polyhedral faces.  This can 
affect some display attributes, such as smooth shading, since the surface 
and curve objects take advantage of knowing the connectivity of the 
objects, which the polyhedral form does not.

The DataFromGroup object has no non-standard directives.