clean the exercisers directory when cleaning everything else

Makefile.in

@@ -167,6 +167,7 @@ echo:   echo.o
 clean:
 	rm -f $(PGMS) $(TESTFRAMEWORK) $(SAMPLE_PGMS) *.o
 	rm -f $(MKDLIB) `./librarian.sh files $(MKDLIB) VERSION`
+	@make -C tests/exercisers clean
 
 distclean spotless: clean
 	@DISTCLEAN@ @GENERATED_FILES@ @CONFIGURE_FILES@ ./mktags ./blocktags

tests/exercisers/Makefile

@@ -14,4 +14,4 @@ run:
 	@for x in $(THINGS); do ./$$x || exit 1; done
 
 clean:
-	rm -f $(THINGS)
+	rm -f $(THINGS) *.o