Bug Fixes and Other Changes

• Added gfile.Open and gfile.Copy, used by input_data.py.
• Fixed Saver bug when MakeDirs tried to create empty directory.
• GPU Pip wheels are built with cuda 7.5 and cudnn-v4, making them
  required for the binary releases. Lower versions of cuda/cudnn can
  be supported by installing from sources and setting the options
  during ./configure
• Fix dataset encoding example for Python3 (@danijar)
• Fix PIP installation by not packaging protobuf as part of wheel,
  require protobuf 3.0.0b2.
• Fix Mac pip installation of numpy by requiring pip >= 1.10.1.
• Improvements and fixes to Docker image.