Use buffered gzip stream with python 2.7.
Use buffered gzip stream with python 2.7.

- Fixes bug 898169.
- It's possible to make GzipFile inherits io.BufferedIOBase in python
  2.6, but IMO it's better let people to use 2.7 if they really need
  this feature.

Change-Id: I4c6e4858e3f616af892e7f4fa6daae0f6ee31723

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