#34: Console reporter improvments

Open issues:
1. I changed the order of the 'update_result' and 'test_hooks' contexts. That way hooks have access to test results (prior to this change, test_error callbacks had to look at sys.exc_info. now they can look at session.get_result).
2. I'm considering a better design for the whole reporting thing:
  * Consider a CaseResult object as parent for Skip, Fail, Pass and Error child classes. each of them will have a short description (like a '.' or a 'F') and long description (like 'ok' or a traceback or a skip reason).
  * Once it's easy to do session.get_result(context.test).description() it'll be easier to implement other plugins that print to a socket or send an email.