Clarify what happens on g.throw(StopIteration).

pep-0479.txt

@@ -72,6 +72,12 @@ again.  The answer is that it from this point on it will raise
 ``StopIteration`` -- the behavior is the same as when any other
 exception was raised by the generator.
 
+Another logical consequence of the proposal: if somone uses
+``g.throw(StopIteration)`` to throw a ``StopIteration`` exception into
+a generator, if the generator doesn't catch it (which it could do
+using a ``try/except`` around the ``yield``), it will be transformed
+into ``RuntimeError``.
+
 
 Consequences for existing code
 ==============================