Made octave link with graphicsmagick to get imread() working.
Nevertheless, imread does not work, because of some problems between octave and latest versions of graphicsmagick: http://www-old.cae.wisc.edu/pipermail/octave-maintainers/2010-February/015295.html
Next to do: add an older version of graphics magick for octave.
svn path=/nixpkgs/trunk/; revision=20389