Pat noted that I neglected to drop the SCCS lines on the files I've been
committing, so clean up those and any others I could find where the SCCS
line date is out of date.
If SHELLDIR is null, don't install nethack.sh. Also a tid in Porting
and add NHSROOT to the Makefiles which gives a path to the top of the
tree (so e.g. you can always find makedefs from a rule in a hints file).
Build and install the NetHack.ad file, and change the nethack.sh to append
the HACKDIR to the XUSERFILESEARCHPATH. This means users do not have to
do anything special to use the NetHack X11 resources, nor does it require
teaching nethack where the X11 app-defaults directory is. The change also
updates the X11 and linux doc files in a corresponding way.
