Element wise sum not working as expected

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What steps will reproduce the problem?
1. Add an element-wise sum layer to your config file.
2. Specify exactly same inputs to the 'inputs' parameter
3. Specify coeffs=1, -1

What is the expected output? What do you see instead?
With exactly same inputs and the coeffs specified as 1 and -1, it is expected 
that the output of the layer produce 0.0
Instead we see a non-zero output. Also changing the coeffs values does not seem 
to have any effect.

What version of the product are you using? On what operating system?
cuda-convnet2 on ubuntu-linux

Please provide any additional information below.

Original issue reported on code.google.com by aniket.v...@gmail.com on 29 Oct 2014 at 11:17