Create a new graph of type `graph-type'. Graph type
can be a symbol naming a sub-class of basic-graph or a list. If it is
a list of symbols naming different classes. If graph-type is a list,
then a class which has all of the listed classes as superclasses will
be found (or created). In either case, the new graph will be created
as if with a call to make-instance.
|make-graph < list >|
|make-graph < symbol >|