HPCC-11261 - fileservice superfile actions can lockup on retry

superfile actions that block due to other locks, clear their
cached files on pause/retry. However, the superfiles from
fileservices were still being held behind the transactions back.
On retry the transaction restablishes the file locks, but is
now in contention with the superfiles held in the caller.

Change so that transaction is started/committed (if required)
after the file is release in the caller

Signed-off-by: Jake Smith <jake.smith@lexisnexis.com>
HPCC-11261 - add some comments

Signed-off-by: Jake Smith <jake.smith@lexisnexis.com>
HPCC-11288 - regression if inside transaction

Signed-off-by: Jake Smith <jake.smith@lexisnexis.com>
Merge pull request #6040 from jakesmith/hpcc-11261-for-4.2.6

HPCC-11261 - fileservice superfile actions can lockup on retry

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>