Inbound cleanup (pep8, indenting, imports).
Inbound: fix security manager problem when not validating sender.
Inbound: add unwrapping setting tests.
Inbound: add secruity tests.
Inbound: use more specific exceptions.
Inbound: extract inbound code into inbound method.
Inbound: extract user getting code into get_user method.
Inbound: refactoring cleanup.
Update changelog.
Fix typo in UnknownSender exception name.
Fix bug when sender is not validated and destination is not public.
Remove "validate_sender" configuration setting.

We always require the sender to be valid.
Merge pull request #15 from 4teamwork/jone-inbound-error-handling

Inbound error handling