Use conda for travis CI

[ajasja]

Conda is a cross-platform packet manger for python that a lot of projects are using wth travis CI. The main advantage over apt-get install python-numpy is that in conda one has a finer control over versions. The ubuntu repo only has numpy 1.6, while 1.8 is the latest stable.

Here are some sample projects using conda:

• https://gist.github.com/dan-blanchard/7045057
• https://gist.github.com/dan-blanchard/7045057