Changes:

- futurize --stage2 changes for Python 3 compatibility by @girving.

- Small updates to documentation by @vrv, schuster and others

- Account for failure of std::thread::hardware_concurrency by @ebrevdo.

- More changes for backwards-compatibility tests by Josh

- Updates to python op doc generation by Josh

- Added support for using the best-fit allocator via ConfigProto by @vrv.

- Rename LocalSession to DirectSession, since local was a bad name for
  it.

- Enable tf.nn.moments() to work with tensors of unknown shape by @mrry.
  GITHUB_ISSUE: 139

- Changes for Android build by Andrew.

Base CL: 107645181