Closes issue #2055. Thanks Giampaolo Rodola.

Closes issue #1960. Thanks Giampaolo Rodola.

Patch from GHOP 294 by David Marek.

Done as GHOP 238 by Josip Dzolonga.

Thanks Benjamin Peterson for the patch.

(Exploit at request.)

Some buildbots were consistently failing (e.g., amd64).
Also remove a couple of semi-colons.

string.

optional: it defaults to the traceback of the exception that is currently
being handled.

Speed up with statements by storing the __exit__ method on the stack instead of in a temp variable (bumps the magic number for pyc files)

SocketServers. The core of the patch was written by Pedro Werneck, but any bugs
are mine. I've also rearranged the code for timeouts in order to avoid
interfering with the shutdown poll.