pgsql-server: Add: * Consider parallel processing a single query

Log Message:
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Add:

* Consider parallel processing a single query

  This would involve using multiple threads or processes to do optimization,
  sorting, or execution of single query.  The major advantage of such a
  feature would be to allow multiple CPUs to work together to process a
  single query.

Modified Files:
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    pgsql-server/doc:
        TODO (r1.1356 -> r1.1357)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/doc/TODO.diff?r1=1.1356&r2=1.1357)