[Mondrian] Adding Grouping Set support for Distinct Count measures

[John V. Sichi]

John V. Sichi wrote:
> I was wondering why the cached runs still took 40s, so I probed the 
> stack and it was spending most of the time in 
> AggregateFunDef.removeOverlappingTupleEntries.  I commented this out, 
> and the LucidDB time went down to 15s for the first execution, and 8s 
> for the cached execution.

In eigenchange 10766, I changed AggregateFunDef to allow it to skip the 
list reduction methods added by Ajit (on a per dialect basis), because 
they are really slow.  Currently it's only skipping for LucidDB, since 
it doesn't have a limit on IN list size, so the reductions aren't 
needed; for dialects where the reductions are required, it would be a 
good idea for someone to optimize Ajit's code.

JVS