It's a bit crude. It always pastes the entire text field, ignoring the
insertion cursor, and ignoring which control really has the focus.
The file dialog, which can call up the Finder, is implemented in the AppKit
so it's not wholly under our control. But I could bolt on an event filter,
after the fashion of CommandManager, to intercept key events.
Perhaps later versions of the toolkit than 10.6 will have a better save dialog
in the AppKit, making this change unnecessary.