40b5b12673
This is an initial round of SAFERHANGUP hangup changes. It introduces SAFERHANGUP, provides the core framework, and enables it for UNIX. Window-port changes are provided for win/tty, win/X11 and win/gnome. Qt changes should be forthcoming after having Warwick look at them. window.doc is updated so windowport maintainers have an clue what needs to be done to support SAFERHANGUP.