[gtkmm] lifetime fix

[Murray Cumming Comneon com]

I have applied this lifetime fix, for a leak when using Glib::wrap(). There
is a risk that it causes other problems, so please try to test the version
in cvs. (gtkmm2 module)
http://bugzilla.gnome.org/show_bug.cgi?id=114568

I will probably release gtkmm 2.2.4 after I have analysed the gcc 3.3 and
debian problems.

Murray Cumming
murrayc usa net
www.murrayc.com