Properly set `attr_accessible` for the model
Properly set `attr_accessible` for the model

We could tell that user uses protected_attributes gem by looking for
`accessible_attributes` method.

Note that there's no test for this. I've tried to add test, but it's
hard to do racing with load order of the files.

Fixes #6

rails/activerecord-session_store,buntine/activerecord-session_store,maclover7/activerecord-session_store,gregmolnar/activerecord-session_store,Partyista/activerecord-session_store,maschwenk/activerecord-session_store