Work around for hpcc-10537 and minor fix to tests

Replace the use of the M of N JOIN with a group rollup to work around problem noted in bug hpcc-10537.  I suspect hat the group rollup is more efficient than the M of N join, though I did use a SORT to assure that the partitions were in the right order.  A MERGE might have been a better choice.

Removed a Byte Order Mark on the Factor test attribute and suppressed a warning in the test difference report attribute.