Re: Incremental sort for access method with ordered scan support (amcanorderbyop)

The v3.1 patch looks good to me, except that the comments around
match_pathkeys_to_index still need some polish.

1. For comment "On success, the result list is ordered by pathkeys.", I
think it'd be more accurate if we say something like "On success, the
result list is ordered by pathkeys or a prefix list of pathkeys."
considering the possibility of incremental sort.

2. The comment below is not true anymore.

   /*
    * Note: for any failure to match, we just return NIL immediately.
    * There is no value in matching just some of the pathkeys.
    */

We should either remove it or change it to emphasize that we may return
a prefix of the pathkeys for incremental sort.

BTW, would you please add the patch to the CF to not lose track of it?

Thanks
Richard