Small update to deal with Chrome flash player, bug in join and check on remember token.

Chrome no longer sends the HTTP_USER_AGENT as Flash, so I've added in a check on HTTP_REFERER for .swf files.

The remember_token check was updated and now sets nil if it is not passed as a param. The associated join on cookie/remember_token did not have the semi-colon escaped (may be a Ruby 1.9 specific change).

Updated Readme with a few additional notes.