pgsql: Improve planner's estimation of the size of an append relation:

Log Message:
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Improve planner's estimation of the size of an append relation: rather than
taking the maximum of any child rel's width, we should weight the widths
proportionally to the number of rows expected from each child. In hindsight
this is obviously correct because row width is really a proxy for the total
physical size of the relation. Per discussion with Scott Carey (bug #4264).

Modified Files:
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pgsql/src/backend/optimizer/path:
allpaths.c (r1.170 -> r1.171)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/path/allpaths.c?r1=1.170&r2=1.171)
pgsql/src/backend/optimizer/plan:
createplan.c (r1.240 -> r1.241)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/plan/createplan.c?r1=1.240&r2=1.241)