Fix logging madness

- Log lymph.ping request as debug
- Workaround gevent to log http requests using python logging (https://github.com/gevent/gevent/issues/106)
I don't think it does use something beside write, and I made it inherit from StringIO just to avoid looking at what weird stuff they are doing there, and as a safety measure, since usually an app should not fail when logging fail (when logging is used correctly e.g. ``logging.info('%s %s', 'a')``) !