Summary:
Added operator RecurrentNetworkBlobFetcherOp that takes as input a scratch workspace name and prefix, and copies over all blobs in the scratch workspace into the global workspace. This essentially extracts all intermediate recurrent network computation for each timestep.
Added a wrapper in recurrent.py - retrieve_step_blobs(net, prefix='rnn') - which, when called after an rnn is run, will return a list of all blobs extracted from the net.
Reviewed By: akyrola
Differential Revision: D5421926
fbshipit-source-id: 0f35b466d77d3c719fb0e32de7dbcafc6c0d5225