Support no-content (204) requests in BasicNetwork.

When we get an empty response for say, a 204, we create a 0 byte
response and pass it on to the NetworkResponse.  Implementers
of Request can then return appropriate Responses.  The behavior
before this change results in an NPE because we attempt to
getContentLength() bytes from a null entity..

Change-Id: Ia5f92ffd99b8f3e88cc92dc50ba43c4721d83e79
Signed-off-by: Ray Colline <rayc@google.com>
make all 2xx be a valid success codes

Change-Id: I94313e2f89c38277d36b7a2aaa525862d2740c98
Merge pull request #3 from tambeti/fixes

Fixes from upstream