This patch makes gcdmaster compile with the new
interfaces provided by sigc++-2.0, gtkmm-2.4, and
It is not tested whether it breakes compatibility with
sigc++-1.2 and gtkmm < 2.4. To get the port compile I
had to disable the AudioCDView::drag_data_received_cb
callback (but appearently it didn't do anything yet),
and the AutoCDProject::Toolbar2() method which is also
not used (as far as I can see) .