correctly test gpu code. The test was disabled by accident.

theano/sandbox/test_neighbours.py

@@ -400,8 +400,13 @@ def test_neibs_grad_verify_grad_warp_centered():
     try:
         unittest_tools.verify_grad(fn, [images_val], mode=mode_without_gpu)
         raise Exception("Expected an error")
+    except NotImplementedError:
+        pass
+
     if cuda.cuda_available:
+        try:
             unittest_tools.verify_grad(fn, [images_val], mode=mode_with_gpu)
+            raise Exception("Expected an error")
         except NotImplementedError:
             pass