HPCC-11786 Roxie cored when processing a file notification

When a CResolvedFile was released (because no query uses it any
more), the subscription to dali for the superfile remained active.
This would result in a core if the superfile was subsequently updated

Also added the ability to disable the superfile subscription system.

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>