ensure a rebuild of include/nhlua.h after fetching Lua source

sys/unix/Makefile.top

@@ -270,6 +270,8 @@ fetch-Lua:
 	( mkdir -p lib && cd lib && \
 	  curl -R -O http://www.lua.org/ftp/lua-$(LUA_VERSION).tar.gz && \
 	  tar zxf lua-$(LUA_VERSION).tar.gz && rm -f lua-$(LUA_VERSION).tar.gz )
+#if we just fetched lua, force include/nhlua.h to be built based on it
+	-rm include/nhlua.h
 
 update: $(GAME) recover $(VARDAT) spec_levs
 #	(don't yank the old version out from under people who're playing it)