mnist demo now works with lmdb and leveldb (set parameter in create_mnist.sh), switched around includes
data now written to backend in batches
minor changes to variable names and error messages + set default backed in convert_mnist_data.cpp to lmdb
updated lenet_train_test.prototxt + minor correction to create_mnist.sh
Merge pull request #1008 from mohomran/mnist_with_lmdb

convert MNIST demo to lmdb, fixes