pgsql: Last week's patch for make_sort_from_pathkeys wasn't good enough:

Log Message:
-----------
Last week's patch for make_sort_from_pathkeys wasn't good enough: it has
to be able to discard top-level RelabelType nodes on *both* sides of the
equivalence-class-to-target-list comparison, since make_pathkey_from_sortinfo
might either add or remove a RelabelType.  Also fix the latter to do the
removal case cleanly.  Per example from Peter.

Modified Files:
--------------
    pgsql/src/backend/optimizer/path:
        pathkeys.c (r1.87 -> r1.88)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/path/pathkeys.c?r1=1.87&r2=1.88)
    pgsql/src/backend/optimizer/plan:
        createplan.c (r1.232 -> r1.233)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/plan/createplan.c?r1=1.232&r2=1.233)
    pgsql/src/backend/optimizer/util:
        tlist.c (r1.74 -> r1.75)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/util/tlist.c?r1=1.74&r2=1.75)
    pgsql/src/include/optimizer:
        tlist.h (r1.45 -> r1.46)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/optimizer/tlist.h?r1=1.45&r2=1.46)