added 'noninherited table' prop to mapper indicating the "lead" table, in the case of

added 'noninherited table' prop to mapper indicating the "lead" table, in the case of
inheritance.  relations now create priamry/secondary joins against that lead table.  if you want to create it against
an inherited table, use explicit join conditions.
added 'correlate' argument to CompoundSelect to get polymorph example working again.