run_parser -> argparser fix in docs.

`run_parser` was renamed to `argparser`: Update the documentation to match.

(Patch from Stephen Thorne.)
Merge branch 'master' of github.com:google/oauth2client
Fix a test with a duplicate name.

Two tests in `test_oauth2client.py` had the same name, meaning one wasn't
getting run. Fixed the name of the second (which now reflects that the test
does indeed test a successful exchange).
Pull from upstream.