Update setuptool (3.4.1 -> 3.4.3)
Add `ironpython-dev`.

I have not yet confirmed the `setuptools` can work together on GNU/Linux though.
Merge branch 'ironpython'
Import recent changess from ruby-build v20140408
Merge branch 'ruby-build-20140408'
Update existing git repo if exists.

The destination repository might exist if the `--keep` was given to
`python-build`.
*EXPERIMENTAL* Add https://github.com/dropbox/pyston