pgsql: Rewrite rewriteTargetList() to avoid O(N^2) behavior on wide

Log Message:
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Rewrite rewriteTargetList() to avoid O(N^2) behavior on wide target lists.

Modified Files:
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pgsql/src/backend/rewrite:
rewriteHandler.c (r1.148 -> r1.149)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/rewrite/rewriteHandler.c.diff?r1=1.148&r2=1.149)