[Mondrian] Adding Grouping Set support for Distinct Count measures

[John V. Sichi]

Julian Hyde wrote:
> Oops. I just realised we were talking about example #2, which is for 
> regular, non-distinct measures. If the MDX set/list contains duplicate 
> members, then the results are added. So I'm instructing delegates to say 
> 'aye' for Matt & Ajit.

I won't argue with MSAS, so double-counting for dups it is.  I'm 
surprised they don't allow you to put on half a state so you can do 
2.5*OR + CA :)

As Ajit points out, this means we have to be careful with pushing down 
constraints for non-distinct aggs to SQL.  Rushan and I have been 
thinking about how to build on the distinct-count optimization she put 
in, with the next step being optimization and caching for non-visual 
totals via calculated members.

JVS