use generators directly instead of relying on the domain to inherit from them, which seems a dubious design

[SVN r62372]

libs/proto

@@ -1 +1 @@
-Subproject commit be01a7f80ed553019dd8a8e1b928d85fab17fe85
+Subproject commit 4b1e5eb2b136bbf660ec9b4efaac1ca4a536d124