Some Octave patches to reapply

These are some patches to the Octave module I would like to reapply. None of them involve whitespace changes or style cleanups. They make the following changes:
- Fix the failures in the Octave Travis builds by disabling optimisation
- Drop support for Octave versions older than 3.2.0
- Test Octave against version 3.8 (the latest stable series) in the Travis builds
I'd prefer to see a standard Ubuntu version tested by default. How about adding in your ppa as a 2nd Octave test? I think it is okay to test 2 versions of one language on Travis if you feel it is useful. It is a shame Octave is so resource heavy though :(