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.
These changes clean up build warnings and allow the resulting "NetHack"
Application icons to be dragged around freely in the Finder, as is expected
for Mac apps.