WIP global: travis fixes

* Adds 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)).
* Downloads the devscripts where they want to be downloaded.
* Moves `apt-get update` to `before_install` as [advised](http://docs.travis-ci.com/user/build-configuration/#Build-Lifecycle)
* Enables the Python 2.6 build, even if it doesn't look like it.

**blockers:**
- [ ] tiborsimko/invenio-devscripts#17
- [ ] bibknowledge requires libxml2 (#1879)
It seems to be still safe assuming you're not using a version from 2009 or youger.

> Do note though that all mod_wsgi 2.X versions prior to mod_wsgi 2.4 do not perform the reordering of 'sys.path' as explained previously, when using WSGIPythonPath directive or 'python-path' option for WSGIDaemonProcess. Thus, you would need to be using WSGIPythonHome to reference a virgin baseline environment when using mod_wsgi 2.3 or earlier if the standard Python site-packages directory has conflicting packages. For mod_wsgi 2.4 onwards this is not an issue and a virtual environments site-packages will always override that in standard Python installation.
> https://code.google.com/p/modwsgi/wiki/VirtualEnvironments

Can we escape the activate setup as well as this dance?
```python
import site
site.addsitedir('/usr/local/pythonenv/PYLONS-1/lib/python2.5/site-packages')
```