Make convert compatible with extensions

Fixes #45 that was prevented extensions from working correctly when the
function was subsequently decorated with the begin.convert() decorator.
This was caused by functools bubbling up the __wrapped__ attribute,
skipping any intermediate functions.
Run continuous integrations tests on Python 3.4

Add Python 3.4 as a build target for Travis-CI.
Make logging tests compatible with Python 3.4

The behaviour of logging.getLevelName() has changed on Python 3.4. For
compatibilty most uses of this function is replaced with getattr().