Add test verifying semantics of idiom for delegate generator wrapping.
Add test verifying semantics of idiom for delegate generator wrapping.

As discussed here:
https://github.com/tc39/agendas/pull/25#issuecomment-33512904

facebook/regenerator,sebmck/regenerator,facebook/regenerator,RReverser/js-goto-transpiler,liviuignat/regenerator,juliocanares/regenerator,RReverser/js-goto-transpiler,rafaelstz/regenerator,facebook/regenerator,sebmck/regenerator,Jericho25/regenerator,kittens/regenerator,rafaelstz/regenerator,kittens/regenerator,liviuignat/regenerator,juliocanares/regenerator,Jericho25/regenerator