Convert Python 3 ResourceWarnings into exception

[Piotr Dobrogost]

Hi!

Recently A. Jesse Jiryu Davis asked at Stackoverflow
(http://stackoverflow.com/q/24717027/95735) if there is "a way to force a
Python 3 unittest to fail, rather than simply print a warning to stderr, if
it causes any ResourceWarning?" Daniel Harding, in the accepted answer,
states it's not possible.

Is it really the case?

For sake of context, here I believe is the place, where
PyErr_WriteUnraisable is being called in this case –
http://hg.python.org/cpython/annotate/c0e311e010fc/Modules/socketmodule.c#l3857