Don't use malloc.h header on OpenBSD.

--- src/ex_cut_round.c.orig	Wed Nov 19 22:57:13 2014
+++ src/ex_cut_round.c	Wed Nov 19 22:57:20 2014
@@ -20,7 +20,6 @@
  */
 
 
-#include <malloc.h>
 #include <math.h>
 #include <stdio.h>
 #include <stdlib.h>
