HPCC-11253 Do not lock superfiles in roxie

When a query is reloaded due to a file change (or a package change, come to
that), any queries that are already in flight may continue to send slave
requests.

By delaying the release of the previous versions fo the slave queries,
in-flight queies should be able to complete.

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