Fixed a TypeError: not enough arguments; expected 4, got 3.
When authentication is needed, the default http_error_401 method calls
retry_http_basic_auth.  The default version of that method expected a
data argument which wasn't provided, so now we provide the argument if
it was given and we also made the data argument optional.

Also changed other calls where data was optional to not pass data if
it was not passed to the calling method (in line with other similar
occurances).