Fixed attribute bug in typeclass swap.
Run migrations! First version of MULTISESSION_MODE=3. @ic/@ooc not working yet.
Implemented a first working version of MULTISESSION_MODE=3
Tested all multisession modes against unittests. Seems to work.
Added clear() method to nattributehandler. Resolves #542.
Fixed some lingering uses of sessid as a non-handler.
Merge branch 'master' of https://github.com/evennia/evennia into FRPI

Updating FRPI branch with changes made to Evennia upstream.