improve error on unqualified Hint

Makefile.coq.local

@@ -15,7 +15,7 @@ test: $(TESTFILES:.v=.vo)
 # Make sure everything imports the options, and all Instance/Argument/Hint are qualified.
 	$(HIDE)for FILE in $(VFILES); do \
 	  if ! fgrep -q 'From stdpp Require Import options.' "$$FILE"; then echo "ERROR: $$FILE does not import 'options'."; echo; exit 1; fi ; \
-	  if egrep '^\s*(Instance|Arguments|Remove|Hint (Extern|Constructors|Resolve|Immediate|Mode|Opaque|Transparent|Unfold))\s' "$$FILE"; then echo "ERROR: $$FILE contains unqualified 'Instance'/'Arguments'/'Hint'."; echo; exit 1; fi \
+	  if egrep '^\s*(Instance|Arguments|Remove|Hint (Extern|Constructors|Resolve|Immediate|Mode|Opaque|Transparent|Unfold))\s' "$$FILE"; then echo "ERROR: $$FILE contains unqualified 'Instance'/'Arguments'/'Hint'."; echo "Please add 'Global' or 'Local' as appropriate."; echo; exit 1; fi \
 	done
 .PHONY: test