Check return type of __nonzero__() method.
Check return type of __nonzero__() method.

The language reference says you must return an int or a bool.  This
fix limits the scope of SF bug 759227 (infinite recursion) to
subclasses of int.

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