make the image2neigs gpu optimization try to move only the version implemented on the gpu.

theano/sandbox/neighbours.py

@@ -654,7 +654,8 @@ def gpu_images2neibs(ten4, neib_shape, neib_step=None, mode='valid'):
 
 @local_optimizer()
 def use_gpu_images2neibs(node):
-    if type(node.op) is Images2Neibs:
+    if (type(node.op) is Images2Neibs and
+        node.op.mode in ['valid', 'wrap_centered']):
         return [host_from_gpu(gpu_images2neibs(gpu_from_host(node.inputs[0]),
                                                node.inputs[1], node.inputs[2],
                                                mode=node.op.mode))]