Use regular attach

Fixes #7, but waiting on https://github.com/dotcloud/docker-py/pull/138. Do not merge yet.

If you want to use these changes now:

1. `pip uninstall fig`
2. checkout https://github.com/orchardup/fig/commit/d150c400bda4b8408ed5e98a2973aff13d8c74af
3. run `python setup.py develop`
4. `pip uninstall docker-py`
5. checkout https://github.com/aanand/docker-py/commit/2450985ac54f8777fb5a5e6cb6b1aceb05a15035
3. run `python setup.py develop`