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/amiga/Makefile.ami

@@ -1583,7 +1583,7 @@ $(O)termcap.o:	$(TTY)termcap.c $(HDEP) $(I)wintty.h $(I)tcap.h
 $(O)topl.o:	$(TTY)topl.c $(HDEP) $(I)wintty.h $(I)tcap.h
 
 $(O)wintty.o:	$(TTY)wintty.c $(HDEP) $(I)wintty.h $(I)tcap.h \
-		$(I)patchlevel.h
+		$(I)date.h $(I)patchlevel.h
 
 $(O)amitty.o:	$(AMI)amitty.c $(HDEP)