[libpng16] Remove pnglibconf.h, pnglibconf.c, and pnglibconf.out instead of

pnglibconf.* in "make clean" (Cosmin).
diff --git a/scripts/makefile.std b/scripts/makefile.std
index 75bb2de..ee6a868 100644
--- a/scripts/makefile.std
+++ b/scripts/makefile.std
@@ -106,7 +106,8 @@
 	chmod 644 $(DESTDIR)$(LIBPATH)/libpng.a
 
 clean:
-	$(RM_F) *.o libpng.a pngtest pngout.png pnglibconf.*
+	$(RM_F) *.o libpng.a pngtest pngout.png pnglibconf.h pnglibconf.c \
+	pnglibconf.out
 
 DOCS = ANNOUNCE CHANGES INSTALL KNOWNBUG LICENSE README TODO Y2KINFO
 writelock: