simplified the forward function code in development branch, we always need to put -n network parameter in command line. Fix this, command line parameter is optional. if provided, will overwrite the setting in config.cfg file.
changed train_net to train_net_prefix in config.cfg, to make it consistent with forward part. This change also simplified the code and is more reasonable.
After setting up the dataset.spec file, the two stage forward pass now can be run with one line of command. The two stage forward pass was tested with a large dataset (1600x1600x89).
add a forward pass test in Travis.