[MONDRIAN-2081] Native sets evaluated with a compound slicer in context are were formerly cached w/o the compound slicer info, hence different compound slicers could
 result in the cached value being incorrectly picked up.

 There was formerly logic which removed multiposition slicers from the cache key altogether, which was likely a carry-over from before we started supporting
 compound slicers in some native eval cases.
Merge pull request #326 from mkambol/mon-2081

[MONDRIAN-2081] Native sets evaluated with a compound slicer in context ...