HPCC-9335 Improvements to single stepping nested merge joins

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
HPCC-9335 Smart stepping join continues to request rows after end of file

Added/tweaked tracing

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge remote-tracking branch 'ghalliday/issue9335' into issue9335

Conflicts:
	roxie/ccd/ccdactivities.cpp

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
HPCC-9335 Improvements to single stepping nested merge joins

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
HPCC-9335 Fix potential core if the input doesn't support stepping

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
HPCC-9335 Smart stepping join continues to request rows after end of file

Stepping information not being returned from single graph result.

Added/tweaked tracing.

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge remote-tracking branch 'ghalliday/issue9335' into issue9335

Conflicts:
	common/thorhelper/thorstep.cpp
	roxie/ccd/ccdactivities.cpp
	testing/ecl/stepping7.ecl
	testing/ecl/stepping7a.ecl
	testing/ecl/stepping7b.ecl
	testing/ecl/stepping7c.ecl
	testing/ecl/stepping7d.ecl
	testing/ecl/stepping7e.ecl
	testing/ecl/stepping7f.ecl
	testing/ecl/stepping7g.ecl
	testing/ecl/stepping7h.ecl

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