Checkpoint: Logistic regression running correctly with 2 nodes.

- Increment Hadoop / Protobuf versions
- Make array_clone pure
Checkpoint: Distributed Logreg working with multiple slaves.

- Amending Forge to be compatible with new dc_size_field and
dc_data_field declarations.

- Adding a custom struct reducer for DenseMatrix
Merge branch 'optiml-clusters' into wip-clusters2