Change gtk2 to gtk3
Change --with-gtk=2.0 to --with-gtk=3.0
Change libunique to libunique3
Change vte to vte3
Change libwnck to libwnck3
Change gtkmm to gtkmm3
Change gtksourceview2 to gtksourceview3
gnome-main-menu is gtk2 only.
Remove unrecognised options.
Build mate-power-manager with GTK3.
Added missing pangox-compat dep.
Fixes for GTK3 build.
Improved build script.