Re #8113. Update PG3Analysis reference result.

It seems that the result changed slightly between my completing #7777 and
it being merged to master.
A tolerance on all the SNSPowderRedux tests is probably a good idea.
Refs #8113 add tolerances
Refs #8113 change tolerances
Merge remote branch 'origin/feature/8113_snspowderredux_small_ref_change'