Issue python#112: Prepare Stackless 3.5, fix PEP479 for Stackless generators

Stackless has its own copy of the gen_send_ex function: slp_gen_send_ex() and gen_iternext_callback(). I added the PEP479 code to gen_iternext_callback().

https://bitbucket.org/stackless-dev/stackless/issues/112

Author: Anselm Kruis

Stackless/core/stacklesseval.c

@@ -967,6 +967,31 @@ gen_iternext_callback(PyFrameObject *f, int exc, PyObject *result)
         }
         Py_CLEAR(result);
     }
+    else if (!result) {
+        /* Check for __future__ generator_stop and conditionally turn
+         * a leaking StopIteration into RuntimeError (with its cause
+         * set appropriately). */
+        if ((((PyCodeObject *)gen->gi_code)->co_flags &
+                                                CO_FUTURE_GENERATOR_STOP)
+            && PyErr_ExceptionMatches(PyExc_StopIteration))
+        {
+            PyObject *exc, *val, *val2, *tb;
+            PyErr_Fetch(&exc, &val, &tb);
+            PyErr_NormalizeException(&exc, &val, &tb);
+            if (tb != NULL)
+                PyException_SetTraceback(val, tb);
+            Py_DECREF(exc);
+            Py_XDECREF(tb);
+            PyErr_SetString(PyExc_RuntimeError,
+                "generator raised StopIteration");
+            PyErr_Fetch(&exc, &val2, &tb);
+            PyErr_NormalizeException(&exc, &val2, &tb);
+            PyException_SetCause(val2, val);
+            PyException_SetContext(val2, val);
+            Py_INCREF(val);
+            PyErr_Restore(exc, val2, tb);
+        }
+    }
 
     /* We hold references to things in the cframe, if we release it
        before we clear the references, they get incorrectly and