CGI::Session::ActiveRecordStore.data_column_name = 'foobar' to use a different session data column than the 'data' default.  References #2731.  Remove error-prone method_missing passthrough to session model.  Cleanup.

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@2944 5ecf4fe2-1ee6-0310-87b1-e25e094e27de