Implement Python2 and 3 `next` methods on cursors.
Partially revert 'Fix permissions in packages'

Review 2081 by @larkost
Merge pull request #3042 from grandquista/grandquista/Python_next

Implement Python2 and 3 `next` methods on cursors.
Merge branch 'next' of https://github.com/rethinkdb/rethinkdb into next