pgsql: Fix cost_nestloop and cost_hashjoin to model the behavior of semi

Log Message:
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Fix cost_nestloop and cost_hashjoin to model the behavior of semi and anti
joins a bit better, ie, understand the differing cost functions for matched
and unmatched outer tuples. There is more that could be done in cost_hashjoin
but this already helps a great deal. Per discussions with Robert Haas.

Modified Files:
--------------
pgsql/src/backend/optimizer/path:
costsize.c (r1.207 -> r1.208)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/path/costsize.c?r1=1.207&r2=1.208)
pgsql/src/backend/optimizer/plan:
createplan.c (r1.258 -> r1.259)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/plan/createplan.c?r1=1.258&r2=1.259)
pgsql/src/backend/optimizer/util:
restrictinfo.c (r1.58 -> r1.59)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/util/restrictinfo.c?r1=1.58&r2=1.59)
pgsql/src/include/optimizer:
restrictinfo.h (r1.43 -> r1.44)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/optimizer/restrictinfo.h?r1=1.43&r2=1.44)