bug#6505: make the Gtk+ port compile with -DGSEAL_ENABLE in preparation for Gtk+-3

[Jan Djärv]

Dan Nicolaescu skrev 2010-06-24 20.34:
> Gtk+-3 will make some structure members private.
>
> Compiling with -DGSEAL_ENABLE points out the problems.
>
> See also http://live.gnome.org/GnomeGoals/UseGseal
> for more info

It is currently not an issue, configure checks for gtk+-2.0, so 3.0 isn't 
considered yet.  Also, other libraries (rsvg, gconf possibly dbus) must also 
be moved forward.

Apart from that, it is the question of how old Gtk+ we should support. 
Currently we say 2.6 (which is really old) or newer.  Most accessor functions 
in Gtk+ where introduced in 2.14, some in 2.16, and in one case, 2.20.

We could add #ifdef:s, but I rather not do that unless we really need to.

That said, I have a private branch that works with Gtk+ 3.0, and some of the 
fixes there can go in the trunk.  Maybe we should bump required to 2.14 and 
get most of the work checked in.

        Jan D.