Ubuntu One backend should check for 402 error for out-of-space messages

[Roman Yepishev]

At the moment here's what is in precise package:

        if status == 400:
            code = log.ErrorCode.backend_permission_denied
        elif status == 404:
            code = log.ErrorCode.backend_not_found
        elif status == 507:
            code = log.ErrorCode.backend_no_space
        else:
            code = log.ErrorCode.backend_error
        return code

Ubuntu One was never using WebDAV-specific 507 code and recently we decided that 402 (Payment Required, as in purchasing more space is required for operation to complete) will be a better fit.

Please update the source to check for 402 error as out-of-space event.