Support GZip compression when fetching discovery URL

[qdii]

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[qdii]

Looks like my last commit broke compatibility with python2, working on a patch…

[qdii]

Should be good now.

[coveralls]

Coverage increased (+0.05%) to 91.747% when pulling adc6c2e on qdii:master into 1211a8d on google:master.

[qdii]

Fixed the lint.

[jameslynnwu]

would be nice to also add deflate support :)

[qdii]

IIUC, it also works with deflate: I just removed the branch as it just repeated what the default branch did. Or am I missing something?

[jameslynnwu]

I expected some code like, https://github.com/httplib2/httplib2/blob/master/python2/httplib2/__init__.py#L521