Attempt to fix windows test failures

Author: pmconrad

test/com/sun/jna/CallbacksTest.java

@@ -375,10 +375,10 @@ public void callback() {
         for (int i = 0; i < Cleaner.MASTER_CLEANUP_INTERVAL_MS / 10 + 5 && (cbstruct.peer != 0 || refs.size() > 0); ++i) {
             // Flush weak hash map
             refs.size();
-            try {
-                Thread.sleep(Cleaner.MASTER_CLEANUP_INTERVAL_MS + 10); // Give the GC a chance to run
+            Thread.sleep(10); // Give the GC a chance to run
+            synchronized (CallbacksTest.class) { // the cbstruct.peer cleanup happens in a different thread, make sure we see it here
                 System.gc();
-            } finally {}
+            }
         }
         assertEquals("Callback trampoline not freed", 0, cbstruct.peer);
     }