Force user to relogin if they timeout on asynchronous call

Route all asynchronous calls through a session checker to make sure the user is logged in and return an error code to the main ajax.send in site.js. If this error code is returned, site.js should redirect the user to the login page with a returnurl of wherever they are.

Currently, if one attacks and their session timed out, the gears just spin and spin and spin with no error.