Different kinds of preprocessing

[chrisrn]

Inside preprocessing.py you are using inception preprocessing to train images and vgg preprocessing for evaluation, according to slim. It's a little bit confusing. If you want to train a different network from inception, then this is not the optimized preprocessing in terms of accuracy. Are you planning to integrate different kinds of preprocessing?

[reedwm]

We do plan on looking into the preprocessing eventually, as part of an effort to converge to good accuracies. See #104 for more information.

Assigning to @bignamehyp for now.