Update checked in version of gsutil to version 4.6

gslib/third_party/oauth2_plugin/oauth2_plugin.py

-from boto.auth_handler import AuthHandler
-from boto.auth_handler import NotReadyToAuthenticate 
-import oauth2_client
-import oauth2_helper
-from gslib.cred_types import CredTypes
-
-IS_SERVICE_ACCOUNT = False
-
-class OAuth2Auth(AuthHandler):
-
-  capability = ['google-oauth2', 's3']
-
-  def __init__(self, path, config, provider):
-    if (provider.name == 'google'
-        and config.has_option('Credentials', 'gs_oauth2_refresh_token')):
-      self.oauth2_client = oauth2_helper.OAuth2ClientFromBotoConfig(config)
-    else:
-      raise NotReadyToAuthenticate()
-
-  def add_auth(self, http_request):
-    http_request.headers['Authorization'] = \
-        self.oauth2_client.GetAuthorizationHeader()
-
-class OAuth2ServiceAccountAuth(AuthHandler):
-  
-  capability = ['google-oauth2', 's3']
-
-  def __init__(self, path, config, provider):
-    if (provider.name == 'google' 
-        and config.has_option('Credentials', 'gs_service_client_id') 
-        and config.has_option('Credentials', 'gs_service_key_file')):
-      self.oauth2_client = oauth2_helper.OAuth2ClientFromBotoConfig(config, 
-          cred_type=CredTypes.OAUTH2_SERVICE_ACCOUNT)
-      
-      # If we make it to this point, then we will later attempt to authenticate
-      # as a service account based on how the boto auth plugins work. This is
-      # global so that command.py can access this value once it's set.
-      # TODO: replace this approach with a way to get the current plugin
-      # from boto so that we don't have to have global variables.
-      global IS_SERVICE_ACCOUNT
-      IS_SERVICE_ACCOUNT = True
-    else:
-      raise NotReadyToAuthenticate()
- 
-  def add_auth(self, http_request):
-    http_request.headers['Authorization'] = \
-        self.oauth2_client.GetAuthorizationHeader()
-