SF bug #963956:   Bad error mesage when subclassing a module
SF bug #963956:   Bad error mesage when subclassing a module

Add a more informative message for the common user mistake of subclassing
from a module name rather than another class (i.e. random instead of
random.random).

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator