python - fe: Implement nowait option.

Log Message:
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Implement nowait option.

This option provides a transaction with the ability to startup and leave prior
to full processing. This allows some applications the ability to avoid some of
the cost of network round-trips.

[In particular, if this feature is taken advantage of, this should help
the performance of installations that have to deal with high latency
connections.]

Modified Files:
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fe/src:
tracenull.py (r1.10 -> r1.11)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/fe/src/tracenull.py.diff?r1=1.10&r2=1.11)