Fix [make headache].

Makefile

@@ -172,7 +172,7 @@ HEADER   := $(shell pwd)/header.txt
 
 .PHONY: headache
 headache:
-	for d in . ; do \
+	for d in benchmark fuzz src test ; do \
 	  $(FIND) $$d -regex ".*\.ml\(i\|y\|l\)?" \
 	    -exec $(HEADACHE) -h $(HEADER) "{}" ";" ; \
 	done