Simple boxing

[Gabriel de Perthuis <Gabriel de-Perthuis laPoste net>]

Hello,
I'm using a GtkTreeModel and I'd like to add some columns (that I won't
display) with some private data. I need a SOME_TYPE macro, so I need a
gobject class for this.
Writing it is annoying, even if I use gob.
Is there a wrapper class that allows me to simply use a gpointer? Are
there memory management problems I should be aware of if I write one, or
is a g_free enough?