Override Twisted's attempt to change warnings.showwarning as part of logging setup.
assertIs is not available on Python 2.6.
Merge pull request #38 from itamarst/uncapture-warnings-37

Override Twisted's attempt to change warnings.showwarning as part of logging setup.

Fixes #37.
Merge remote-tracking branch 'origin/master' into timeouts-by-default-36