GUI integration

[John W. Eaton]

I checked in the following change on the GUI branch:

  http://hg.savannah.gnu.org/hgweb/octave/rev/bfc220d1de67

Now when you build Octave (on the GUI branch), ./run-octave will start
the GUI when Octave is running interactively.

We have two new options for Octave:

  --no-gui       disable the gui

  --force-gui    force the gui to start, even when executing
                 commands from a file or processing an --eval string

There is also a separate binary, octave-cli that is not linked with
the gui libraries.  This allows you to save memory and startup time
when you don't plan to use the gui.

Note that this is still a work in progress.  If you are compiling
Octave in a clean build tree, you will need to do the following after
running configure

  make -C src interp-core/mxarray.h

This extra step is needed because the GUI currently includes files
that need mxarray.h but that file is generated as part of building
the liboctinterp library.  I'm looking at making some changes so that
it will not be necessary to manually generate mxarray.h.

jwe