[MONDRIAN-1572] Optimize join paths for Many to Many Dimensions, their
intermediate m2m parent hierarchies are not necessary as part of the join
path.  Note that this feature is being left in experimental mode due to
scenarios where removing the intermediate join might actually slow down
performance due to joining one large fact table to another directly vs.
indirectly through a smaller dimension table.  Once a larger regression is
ran against this feature we will remove the experimental designation.