update runtime docs, thanks @uniphil!

#117
fix url to testing buildpack
Merge pull request #118 from uniphil/master

fix url to testing buildpack
Use a sed() function for unbuffered output.

In `bin/steps/collectstatic` the unbuffered output in `indent` is subverted
by calling `sed` first:

```shell
python $MANAGE_FILE collectstatic --noinput  2>&1 | sed '/^Copying/d;/^$/d;/^ /d' | indent
```

This commit fixes this by making `sed` itself unbuffered rather than
putting that logic in the `indent` function.
Update to Setuptools 2.1 and Pip 1.5.2

So seamless.
Merge remote-tracking branch 'origin/master'
--allow-all-external
pip v1.5.4
Update Readme.md
Merge pull request #120 from agriffis/sed-func

Use a sed() function for unbuffered output.
Install extra reqs from env var.

Set PYTHON_EXTRA_REQS to a newline-separated list of packages, exactly
like you might find in requirements.txt, to have them installed into the
slug.