Re: FETCH FIRST clause WITH TIES option

I rebased this patch, and my proposed changes are in 0002.

Looking at the changes in ExecLimit, I'm wondering if it would be better
to add a new state to the state machine there -- instead of doing all
the work in duplicative code in the LIMIT_INWINDOW case, have that one
only save the current end-of-window tuple and jump to
LIMIT_WINDOWEND_WITH_TIE (or something) which then returns all tuples that
match the current one.  I think that would end up being cleaner.  Please
research.