Add a command or other mechanism by which unresolved references
can be viewed, and/or assistance in resolving them.

Requested by S. Marks:
"* Regarding forward references, clearly JShell keeps track of references that are currently unsatisfied. Is there a way to see these? I can list methods with /methods and look for ones which have a "cannot be invoked" line, but it would be good if there were a way to list just the ones with unsatisfied forward references."