Wrapped the input and gradOutput by a table, if only one input or gradOutput is used.
Simplified the code.
Removed unused function.
Used common code to get the gradOutput.
Kept only gradients to sum inside of the data.gradOutput.
Clarified the meaning of innode.data.gradOutput.
Reused the computed gradOutputBuffer.
Merge pull request #8 from fidlej/topic_data_oblivious

Using data.gradOutput to hold the to-be-summed gradients