I don't think this should be part of the pull request. This PR is for the back button, and this exit function is added without being used. This is probably better off in another pull request.

Second off, this isn't really the way to exit an app as the MSDN page suggests: http://msdn.microsoft.com/en-us/library/windowsphone/develop/system.windows.application.terminate(v=vs.105).aspx

>"Otherwise, apps should not use this method to provide an “Exit” mechanism. The Terminate method does not raise any application lifecycle events."

I haven't looked into the 'proper' closing of an app on WP8, but if there's no better way around this then at the very least we need to make sure that our Exiting events are triggered before Terminate().