Fix the test_bayes tests into a working state. (#84)
Fix the test_bayes tests into a working state. (#84)

It seems the test_bayes tests has not worked for a long time. This
diff makes the test run on my machine with the following changes:
* Removed the msgid and receive_date tests, as the code they are
testing moved to oa/message.py. The tests are submitted in updated
form in https://github.com/SpamExperts/OrangeAssassin/pull/83
* Updated learn_message test to the new call signature of
_learn_trapped
* Have the setUp get_engine() reflect the module remname pad -> oa
SpamExperts/OrangeAssassin