Change float in test_ConvTrans and test_ConvUnify to real.

* The DataProvider should be INCREF every time.

* But not reproduce the problem.

Added a test in test_NetworkCompare to verify cudnn and exconv, fixed a bug in cudnn_conv in dealing with groups

The instance weight and coeff are only mulipled to the gradient with respect to input.

out = w * input
where w is a parameter of size 1

Change-Id: Ife682d62323ceb1a20cbbf6269421b20a862d888