multi line cell edition

[Nicolas Soubeiran <nicolas soubeiran gmail com>]

Hi all, I need to edit a "multi-line" cell in a treeview.
GtkCellRendererText can display a "multi-line" text, I need to be able
to edit it and/or let the user set a multi line value in the cell.
I look at GtkEntry APIs and I found gtk_entry_get_layout* API but I
have no idea on how I can use it. Or have I to create a custom widget?
How can I do this? I'm working on a GTK+ 2.18 version (RedHat 6)
Thanks