[MONDRIAN-2072]  When a virtual cube uses a compound slicer with unrelat...

...ed dimensions, invalid results occur

This change is a merge of Will's commit (https://github.com/wgorman/mondrian/commit/953037d879bba35a31f330d8e71d6fbab5b3ae50),
plus tests to verify functionality.  The commit also addresses the case where a measure is present in the slicer, which was not covered by Will's original commit.