display version and build info at startup (trunk only)

Tested on the unix port; I've updated as many other ports as I can figure
out but they're not tested.  See window.doc for info on the changed banner
lines.  Also adds the ability to override the generic "Unix" port - used now to get
"MacOSX" into the version line instead of "Unix" (so we don't scare people who don't
know what's going on).

sys/msdos/Makefile.MSC

@@ -988,7 +988,7 @@ termcap.o: $(WIN)\termcap.c $(HACK_H) $(INCL)\tcap.h
 topl.o: $(WIN)\topl.c $(HACK_H) $(INCL)\tcap.h
 	@$(CC) $(CFLAGS) $(SPECOPTS) /Fo$@ $(WIN)\topl.c
 wintty.o: $(WIN)\wintty.c $(HACK_H) $(INCL)\dlb.h \
-		$(INCL)\patchlev.h $(INCL)\tcap.h
+		$(INCL)\date.h $(INCL)\patchlev.h $(INCL)\tcap.h
 	@$(CC) $(CFLAGS) $(SPECOPTS) /Fo$@ $(WIN)\wintty.c
 
 # src dependencies