Add missing include needed to run tests which use usleep

--- clucene-core-2.3.3.4/src/test/test.h	2011-03-17 00:21:07.000000000 +0000
+++ clucene-core-2.3.3.4/src/test/test.h	2017-12-27 09:43:25.320000000 +0000
@@ -23,6 +23,7 @@
 #include <iostream>
 #include <string.h>
 #include <stdio.h>
+#include <unistd.h>
 
 using namespace std;