* bzrlib/smtp_connection.py: (SMTPConnection._authenticate): Try the authentication config before prompting the user.
* bzrlib/tests/test_smtp_connection.py: Fix some imports. (everybody_is_welcome): Fake auth smtp server. (TestSMTPConnection): Now inherits from tests.TestCaseInTempDir so that we can create an authentication.conf in a protected env. (TestSMTPConnection.test_smtp_password_from_auth_config): New test. (TestSMTPConnectionWithUI): New test for prompting user.