$OpenBSD$
Unbreak build.
--- src/plugin.c.orig	Wed Nov 23 08:54:28 2016
+++ src/plugin.c	Wed Nov 23 08:54:38 2016
@@ -25,6 +25,8 @@
  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+#include <sys/select.h>
+
 #include "plugin.h"
 #include "utils.h"
 
