Handle expiry correctly in json response

Go treats json numbers as float64 not int. Previously json response
expiry information was ignored since it was expected to be an int.
Merge pull request #50 from snikch/fix-json-expiry

Handle expiry correctly in json response
oauth2: add vanity URL import comments, use the vanity URL on builds

Change-Id: Ia20e40d98aa709e3d598388e0a15501584152ab5
Merge branch 'master' of https://github.com/golang/oauth2
Merge remote-tracking branch 'golang/master'