major changes

passport.socketio now lets the user decide whether to accept a
connection or not. to do so, you have tu provide your own 'fail'-method.
this will be called unless the user is successfuly authenticated (still
uses the 'success'-method). The method will be called with four
parameters:
- data: <Object> Handshake Data
- message <String> Error-Message
- critical <Bool> True if the User is and will be unable to use
socket.io because of errors in the authorization-system or somewhere
else. False if the user would still be able to use the system (indicates
that he's just not logged-in)
- accept: <function> plain old accept function.
If there's no fail-method given, passport.socketio allows every
not-critical-failed connection.
Also there is now a 'logged_in' <Bool>-Property inside your User-Key.