Signal/slot paradigm in graphics code, libsigc++ dependency

[Michael Goffioul]

Hi,

I was thinking about implementing a more formal signal/slot paradigm in
the graphics code to take care of the property/object listeners and builtin
updaters. While trying to figure the implementation specs, I remembered
of the libsigc++ library that already provides such complete framework.

I didn't check everything, but I think it provides everything I'd need. So would
it be acceptable to use it within octave, adding (yet) another dependency?

Michael.