Delegating generators do not show always up in stack traces, such as inspect.stack().
The show up during the first delegation, but not thereafter.

I have attached a patch. It alters the way the YIELD_FROM bytecode works; it loops back on itself. This ensures the delegator's frame is always in the trace.

Unfortunately I started working on it before Benjamin fixed issue 14220
(rev 3357eac1ba62). By the nature of it, this patch necessarily fixes most of issue  14220, so I have just included the tests for issue 14220
in this patch as well.
So in order to apply this, 3357eac1ba62 will have to be backed out.
Sorry for the overlap.