Fix cli for python 2.6

Right now fig is unusable on python 2.6.

Error:
```
$ fig
Traceback (most recent call last):
  File ".../.tox/py26/bin/fig", line 9, in <module>
    load_entry_point('fig==0.5.0', 'console_scripts', 'fig')()
  File ".../.tox/py26/lib/python2.6/site-packages/fig/cli/main.py", line 27, in main
    console_handler = logging.StreamHandler(stream=sys.stderr)
TypeError: __init__() got an unexpected keyword argument 'stream'
```

This fixes the issue, adds a test, and cleans up the tox.ini to install dependencies properly.

As a side question, why does `CONTRIBUTING.md` suggest using `scripts/test` instead of `tox -e py27` or something like that?