Created by: lcy-seso

实现 Op 时难免出现梯度检查不过的情况，发现目前 Gradient Check 的输出信息还是过于简陋，下面是出错信息。

可以输出更多信息，比如：一共多少维度，多少维度有diff，多少维度没有diff，diff值有多少。方便对整体出错情况有一个判断。

.F
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FAIL: test_check_output (__main__.TestSoftmaxWithCrossEntropyOp)
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Traceback (most recent call last):
  File "test_softmax_with_cross_entropy_op.py", line 33, in test_check_output
    self.check_output()
  File "/home/caoying/paddle_codes/paddle_github/python/paddle/v2/framework/tests/op_test.py", line 207, in check_output
    self.check_output_with_place(place)
  File "/home/caoying/paddle_codes/paddle_github/python/paddle/v2/framework/tests/op_test.py", line 200, in check_output_with_place
    "output name: " + out_name + " has diff.")
AssertionError: output name: Loss has diff.