purePackages.octave: Use octaveHg

Pure's Octave package compiles but crashes with Octave 4.2 due to an
upstream bug which is fixed in mercurial.

pkgs/development/pure-modules/octave/default.nix

@@ -19,7 +19,9 @@ stdenv.mkDerivation rec {
     description = "An Octave module for the Pure programming language";
     homepage = http://puredocs.bitbucket.org/pure-octave.html;
     license = stdenv.lib.licenses.gpl3Plus;
-    platforms = stdenv.lib.platforms.linux;
+    # This is set to none for now because it does not work with the
+    # current stable version of Octave.
+    platforms = stdenv.lib.platforms.none;
     maintainers = with stdenv.lib.maintainers; [ asppsa ];
   };
 }