Don't use malloc.h header on OpenBSD.

--- src/segment.c.orig	Wed Nov 19 22:59:20 2014
+++ src/segment.c	Wed Nov 19 22:59:27 2014
@@ -16,7 +16,6 @@
  * Copyright (c) 1991,1993,2003 Linas Vepstas <linas@linas.org>
  */
 
-#include <malloc.h>
 #include <stdlib.h>
 #include <math.h>
 #include <string.h>	/* for the memcpy() subroutine */
