[MONDRIAN-1226] Set on slicer axis with different behaviour than aggrega...

...ted member of same set in the slicer.  Modified so that the calculated members which override context are treated correctly in the scenario in the defect:  if the overriden member is from the first hierarchy found in the compound slicer's tuple list.  If there is more than one hierarchy in the slicer there is still the possibility that calc members which override context won't be handled correctly.  See _test1226Variation for an example.

@lucboudreau let me know if there's any further changes.