[PATCH] Shutdown runners

This begins the shutdown sequence cleanup by creating a Runners Registry
hook at the begining of the shutdown process.

This registry is for use by components which need to cleanup state or
begin some process which happens during the shutdown_timeout period.

The existing code closing server ports and de-registering authentication
schemes has been converted to runners.

NOTE: There is some doubt over the auth runner, as the state being
closed may still be needed for as yet unprocessed client requests on
existing connections. However this is what the current trunk code does
so have left the behaviour as-is for now.

Amos