replace some weight-related magic numbers

adds a header file include/nhconst.h  (I'm open to a better name)

sys/vms/Makefile.src

@@ -393,7 +393,7 @@ $(HACK_H) : $(INC)hack.h $(CONFIG_H) $(INC)align.h \
 		$(INC)dungeon.h $(INC)sym.h $(INC)defsym.h $(INC)mkroom.h \
 		$(INC)objclass.h $(INC)youprop.h $(INC)prop.h \
 		$(INC)permonst.h $(INC)monattk.h \
-		$(INC)monflag.h $(INC)mondata.h $(INC)pm.h \
+		$(INC)monflag.h $(INC)mondata.h $(INC)nhconst.h $(INC)pm.h \
 		$(INC)wintype.h $(INC)context.h $(INC)decl.h $(INC)quest.h \
 		$(INC)spell.h $(INC)color.h $(INC)obj.h \
 		$(INC)you.h $(INC)attrib.h $(INC)monst.h \