refs #5872 Increased accuracy of Box tree loaders and

modify the CompareMDWorkspaces to check reller rather then abserr on large data.

This is because system test requesting 10-5 accuracy was failing on comparing boxes volumes.

The ultimate solution would be the changes in MDBox structure but it is subject to another ticket.
Merge branch 'defect/5872_SliceMDInterupt' into develop