Add a chroot install hints file for linux

This makes installing NetHack on a public server much easier.
Required some minor changes to the unix top-level Makefile, and
the other hints files; Makefile variable HACKDIR may not be a
full path anymore, use INSTDIR instead.

sys/unix/hints/macosx

@@ -72,7 +72,7 @@ WINOBJ += $(WINX11OBJ)
 WINLIB += $(WINX11LIB)
 LFLAGS=-L/usr/X11R6/lib
 VARDATND = x11tiles NetHack.ad pet_mark.xbm
-POSTINSTALL= bdftopcf win/X11/nh10.bdf > $(HACKDIR)/nh10.pcf; (cd $(HACKDIR); mkfontdir)
+POSTINSTALL= bdftopcf win/X11/nh10.bdf > $(INSTDIR)/nh10.pcf; (cd $(INSTDIR); mkfontdir)
 CFLAGS += -DX11_GRAPHICS
 endif
 
@@ -107,6 +107,8 @@ ifdef WANT_SHARE_INSTALL
 PREFIX:=/Users/$(GAMEUID)
 SHELLDIR=$(PREFIX)/bin
 HACKDIR=$(PREFIX)/nethackdir
+INSTDIR=$(HACKDIR)
+VARDIR=$(HACKDIR)
 CHOWN=chown
 CHGRP=chgrp
 # We run sgid so the game has access to both HACKDIR and user preferences.
@@ -116,12 +118,14 @@ VARDIRPERM = 0775
 ROOTCHECK= [[ `id -u` == 0 ]] || ( echo "Must run install with sudo."; exit 1)
 # make sure we have group GAMEUID and group GAMEGRP
 PREINSTALL= . sys/unix/hints/macosx.sh user $(GAMEUID); . sys/unix/hints/macosx.sh group $(GAMEGRP); mkdir $(SHELLDIR); chown $(GAMEUID) $(SHELLDIR)
-POSTINSTALL= touch $(HACKDIR)/sysconf; $(CHOWN) $(GAMEUID) $(HACKDIR)/sysconf; $(CHGRP) $(GAMEGRP) $(HACKDIR)/sysconf; chmod $(VARFILEPERM) $(HACKDIR)/sysconf
+POSTINSTALL= touch $(INSTDIR)/sysconf; $(CHOWN) $(GAMEUID) $(INSTDIR)/sysconf; $(CHGRP) $(GAMEGRP) $(INSTDIR)/sysconf; chmod $(VARFILEPERM) $(INSTDIR)/sysconf
 CFLAGS+=-DSYSCF -DSYSCF_FILE=\"$(HACKDIR)/sysconf\" -DSECURE
 else
 PREFIX:=$(wildcard ~)
 SHELLDIR=$(PREFIX)/bin
 HACKDIR=$(PREFIX)/nethackdir
+INSTDIR=$(HACKDIR)
+VARDIR=$(HACKDIR)
 CHOWN=true
 CHGRP=true
 GAMEPERM = 0700