They show up as checkable GButtons in GToolBar, and with (or without) check
marks in menus.
There are a bunch of places to make use of this. This patch only takes
advantage of it in the FileManager for the view type actions.
This is useful for static locals that never need to be destroyed:
Thing& Thing::the()
{
static Eternal<Thing> the;
return the;
}
The object will be allocated in data segment memory and will never have
its destructor invoked.
In other words, if a surface stretches from the left side of the window
all the way to the right side, skip shading and highlighting the sides.
This makes widgets blend together just slightly with the window. :^)
