[gtkmm] Breaking unused API/ABI.

[murrayc t-online de (Murray Cumming)]

GTK+ has broken API and ABI for some GtkTreeView signals, by changing
their return types. This breaks the gtkmm build and would break it at
runtime if it did build.

These are "key-binding" signals, such as "select-all" and
"toggle-cursor-row", that nobody needs to use anyway - that's why the
GTK+ developers thought it was acceptable. We plan to do the same thing
in gtkmm 2 - we will break this part of the API. In the future we will
not wrap these particular signals.

-- 
Murray Cumming
murray usa net
www.murrayc.com