chef.fabric (and probably other places) are missing `from __future__ import absolute_import`

[Julian]

It looks like these were dropped in 0.3.0, but that breaks lots of things -- e.g. chef_environment no longer works (in fabfiles that define their own non-legacy tasks) because there's a try/except on from fabric.api import env, task, roles, output, which will raise an ImportError because fabric will be chef.fabric, and then the except block then has task being a passthrough, but that doesn't work, fabric will ignore legacy tasks if a fabfile defines its own. I'd guess the behavior of that try/except might be worth changing on its own too, but apologies if I've missed anything.