Added calls to the ToApp and ToAdmin callbacks on the application object from within session.  This is needed for applications that need to provide authentication credentials (username and password) on the Logon message, for example.
Changed checksum calculation in Message and MessageBuilder to include Body length tag in calculation
Merge pull request #35 from pfeairheller/fix/call_to_session_to_admin

Added calls to the ToApp and ToAdmin callbacks on the application object from within session
Merge pull request #36 from pfeairheller/fix/message_checksum

Changed checksum calculation in Message and MessageBuilder to include Body length tag