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
Done. The version of Travis (3.2) is fairly old - Debian stable is at 3.6, Debian testing and recent Ubuntu are at 3.8. So it would be nice to also see a newer version tested, so long as it doesn't slow down the Travis builds too much. I agree that the long compile times are a pain!