New shutdown handler

[WinterSilence]

Need extend or replace method Kohana::shutdown_handler() for adding handlers for other classes (__destruct() is sometimes unstable).

As example my class ShutdownHandler.

[acoulton]

You mean so that applications can add their code to a stack to be run by us, rather than calling register_shutdown_function directly? Sounds interesting. Presumably we could make this relatively BC.

[WinterSilence]

Yes, shutdown stack. Pluses: attenuated depending to Kohana_Core, adding to top of list.