Fix tests in DebugMode with DNN convolutions

theano/sandbox/cuda/dnn.py

@@ -158,9 +158,16 @@ class GpuDnnConvDesc(GpuOp):
         if kern_shape.type.ndim != 1 or kern_shape.type.dtype != 'int64':
             raise TypeError('kern must be 1D shape tensor')
 
-        return Apply(self, [img_shape, kern_shape],
+        node = Apply(self, [img_shape, kern_shape],
                      [CDataType("cudnnConvolutionDescriptor_t",
                                 freefunc="cudnnDestroyConvolutionDescriptor")()])
+        # DebugMode cannot compare the values of CDataType variables, so by
+        # default it returns False all the time. To prevent DebugMode from
+        # complaining because of the MergeOptimizer, we make this variable
+        # always compare to True.
+        out = node.outputs[0]
+        out.tag.values_eq_approx = tensor.type.values_eq_approx_always_true
+        return node
 
     def c_code(self, node, name, inputs, outputs, sub):
         img_shape, kern_shape = inputs