Don't use malloc.h header on OpenBSD.

--- stocks/currency.c.orig	Thu Nov 20 01:56:30 2014
+++ stocks/currency.c	Thu Nov 20 01:56:37 2014
@@ -23,7 +23,6 @@
 
 #include <stdio.h>
 #include <string.h>
-#include <malloc.h>
 #include <stdlib.h>
 
 #include "stocks.h"
