Login failure needs better error message

[headlessme]

Andys-MacBook-Air-2:yotta andy$ yotta login headlessme
Enter the password for github user headlessme:
Traceback (most recent call last):
  File "/usr/local/bin/yotta", line 9, in <module>
    load_entry_point('yotta==0.0.11', 'console_scripts', 'yotta')()
  File "build/bdist.macosx-10.9-x86_64/egg/yotta/main.py", line 87, in main
  File "build/bdist.macosx-10.9-x86_64/egg/yotta/login.py", line 10, in execCommand
  File "build/bdist.macosx-10.9-x86_64/egg/yotta/lib/github_access.py", line 126, in authorizeUser
  File "/usr/local/Cellar/python/2.7.6/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/restkit/resource.py", line 144, in post
    headers=headers, params_dict=params_dict, **params)
  File "/usr/local/Cellar/python/2.7.6/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/restkit/resource.py", line 210, in request
    response=resp)
restkit.errors.RequestFailed: {"message":"Validation Failed","documentation_url":"https://developer.github.com/v3/oauth_authorizations/#create-a-new-authorization","errors":[{"resource":"OauthAccess","code":"already_exists","field":"description"}]}

[autopulated]

This failure is caused by a limited number of authentication tokens being available for each application.
The right way to fix it is to request to retrieve an existing token, if one exists, instead of generating a new one.

[autopulated]

This is no longer an issue with the new login flow