Merging in LYH's GSoC work

[Jordi Gutiérrez Hermoso]

Stefan Mahr has been working on integrating LYH's work into Octave:

    http://inversethought.com/hg/octave-nkf/graph/test-jit

(warning: this repo is test-driving hg's Evolve extension. If you pull
from it repeatedly, you may apparently get the repeated copies of the
same commits as we keep editing this. Enable Evolve on your local hg
to omit the repeated edits.)

I'm about to pull this into Savannah, up until the lyh-rework
bookmark. Stefan isn't sure about the commit under the test-jit
bookmark, but it looks ok to me, as long as JIT isn't enabled by
default.

Can we get some code review of the rest before pulling this into
Savannah?

- Jordi G. H.