This make possible to apply private issues or rietveld instances requiring
authentication.

Forces simplejson to be installed or uses python 2.6's json

Make local_rietveld.py usable standalone.

R=dpranke@chromium.org
TEST=unit tests + manual testing, owners.sh is currentl broken, unrelated to this change.
BUG=none

Review URL: http://codereview.chromium.org/6721031

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@79734 0039d316-1c4b-4281-b951-d872f2087c98