Add header for OS X.

This commit was SVN r17924.

opal/event/kqueue.c

@@ -49,6 +49,9 @@
 #ifdef HAVE_INTTYPES_H
 #include <inttypes.h>
 #endif
+#ifdef HAVE_UTIL_H
+#include <util.h>
+#endif
 
 /* Some platforms apparently define the udata field of struct kevent as
  * intptr_t, whereas others define it as void*.  There doesn't seem to be an