python - pq: Refine extended protocol transactions.

Log Message:
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Refine extended protocol transactions.

The extended protocol messages require that a FlushMessage is sent to
"terminate the operation". With one message per flush, extended protocol
transactions can be quite taxing. To ease this, reorganize the extended query
transactions so that the base single message transactions can be easily
inherited to create compound transactions with a single Flush. Three new
compound transactions appear at the end of client3.

Also, remove the unused rob.notices list from client3.Transaction.

Modified Files:
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    pq/src:
        client3.py (r1.4 -> r1.5)
        (http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/pq/src/client3.py.diff?r1=1.4&r2=1.5)
    pq/test:
        client3.py (r1.3 -> r1.4)
        (http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/pq/test/client3.py.diff?r1=1.3&r2=1.4)