PEP 342 implementation.  Per Guido's comments, the generator throw()
method still needs to support string exceptions, and allow None for the
third argument.  Documentation updates are needed, too.
diff --git a/Include/graminit.h b/Include/graminit.h
index a46cdc9..2c855ea 100644
--- a/Include/graminit.h
+++ b/Include/graminit.h
@@ -76,3 +76,4 @@
 #define gen_if 331
 #define testlist1 332
 #define encoding_decl 333
+#define yield_expr 334