Added include protection for unistd.h and sys/time.h.

diff --git a/scheduler/syslevel.c b/scheduler/syslevel.c
index feb3a9b..974650d 100644
--- a/scheduler/syslevel.c
+++ b/scheduler/syslevel.c
@@ -18,7 +18,11 @@
  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  */
 
-#include <unistd.h>
+#include "config.h"
+
+#ifdef HAVE_UNISTD_H
+# include <unistd.h>
+#endif
 #include <sys/types.h>
 #include "ntddk.h"
 #include "syslevel.h"