pgsql: Back out prior patch and instead just suppress SubqueryScan

Log Message:
-----------
Back out prior patch and instead just suppress SubqueryScan elimination
when there are extra resjunk columns in the child node.  I found some
additional cases involving Append nodes that weren't handled by the
prior patch, and it's not clear how to fix them in the same way without
breaking inheritance cases.  So the prudent path seems to be to narrow
the scope of the optimization.

Modified Files:
--------------
    pgsql/src/backend/optimizer/plan:
        setrefs.c (r1.113 -> r1.114)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/plan/setrefs.c.diff?r1=1.113&r2=1.114)