Bug 455940 - Blow away the dist directory for top level makes

r=bsmedberg

Makefile.in

@@ -49,6 +49,7 @@ default alldep all::
 	$(RM) -rf $(DIST)/include
 	$(RM) -rf $(DIST)/private
 	$(RM) -rf $(DIST)/public
+	$(RM) -rf $(DIST)/dist/bin
 	$(RM) -rf _tests
 
 TIERS += base