pgsql: Avoid useless work during set_plain_rel_pathlist() when the

Log Message:
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Avoid useless work during set_plain_rel_pathlist() when the relation
will be excluded by constraint exclusion anyway. Greg Stark

Modified Files:
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pgsql/src/backend/optimizer/path:
allpaths.c (r1.161 -> r1.162)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/path/allpaths.c.diff?r1=1.161&r2=1.162)