- Fix segfault with invalid coding.

- SF Bug #772896, unknown encoding results in MemoryError, which is not helpful

I will only backport the segfault fix.  I'll let Anthony decide if he wants
the other changes backported.  I will do the backport if asked.

Parser/pgenmain.c

@@ -116,6 +116,13 @@ getgrammar(char *filename)
 	return g;
 }
 
+/* Can't happen in pgen */
+PyObject*
+PyErr_Occurred()
+{
+	return 0;
+}
+
 void
 Py_FatalError(const char *msg)
 {