global: travis fixes

* Adding the language key (otherwise, [it's ruby](http://docs.travis-ci.com/user/getting-started/#Step-three%3A-Add-.travis.yml-file-to-your-repository)).
* Downloading the devscripts where they want to be downloaded.
* Moving `apt-get update` to `before_install` as [advised](http://docs.travis-ci.com/user/build-configuration/#Build-Lifecycle)

**NB** with that change, the build is effectively using Python 2.6 and not the default version, probably 2.7.