[gtkmm] Setting relief style of Gtk::ToolButton

[Chris Vine <chris cvine freeserve co uk>]

I notice that Gtk::ToolButton inherits a get_relief_style() method from 
Gtk::ToolItem, which returns a Gtk::ReliefStyle enumeration.  Gtk::ToolBar 
contains a similar get_relief_style() method, which also returns a 
Gtk::ReliefStyle enumeration.

However, there does not not appear to be a means of directly setting the 
relief style.  The documentation refers to Gtk::Button::set_relief() (and the 
C documentation does likewise in relation to gtk_button_set_relief_style()), 
but this is irrelevant because because Gtk::ToolButton does not inherit from 
Gtk::Button.

Can anyone tell me how this is done?

Chris.