HPCC-8890 - Avoid early abort losing original error

An early error from slave to master, caused graph execution
code to spot the abort condtion and fire a new spurious error,
losing the original.

Also add a better mechanism to abort in-flight receivers.

Signed-off-by: Jake Smith <jake.smith@lexisnexis.com>
Merge pull request #4031 from jakesmith/hpcc-8890

HPCC-8890 - Avoid early abort losing original error

Reviewed-By: Gavin Halliday <gavin.halliday@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>
HPCC-8585 Ensure Priority is cloned into the workunit

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>