pgsql: cost_agg really ought to charge something per output tuple; else

Log Message:
-----------
cost_agg really ought to charge something per output tuple; else there
are cases where it appears to have zero run cost.

Modified Files:
--------------
pgsql/src/backend/optimizer/path:
costsize.c (r1.146 -> r1.147)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/path/costsize.c.diff?r1=1.146&r2=1.147)