[container] send_and_wait safety considerations

[gkistler]

Per our IRC chat, making this stub to remind us to look over potential issues with send_and_wait, especially with regards to exceptions inside the calling loop.

e.g. an exception here might do bad things.

[Clam-]

Some interesting information is available here at the bottom of the page:
http://pypy.org/compat.html
I think a similar thing might happen under CPython, or something.