cmemcache_hash: Encode key to bytes
Use six.iteritems
check_key: Auto-convert unicode keys to bytes for better Python 3
compat

It would be a bit of a pain (and ugly) in Python 3 to have to prefix all
literal keys with the "b" literal notation for bytes.
setup.py: Duplicate version so we don't have to import memcache

This will fail if memcache imports dependencies that are not installed
yet, like `six`.
Merge pull request #1 from msabramo/py33_fixes

Py33 fixes