queue: Make join not wait if there are no unfinished tasks

This fixes GitHub issue #54
support: bundle six 1.5.2

https://bitbucket.org/gutworth/six
http://pythonhosted.org/six/
python3 compat fixes

https://github.com/eventlet/eventlet/pull/59
travis: Build with Python 3.3
greenio: check both EAGAIN and EWOULDBLOCK; Thanks to Ramakrishnan G

https://github.com/eventlet/eventlet/issues/61