python - pq: Implement COPY support in Executing.

Log Message:
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Implement COPY support in Executing. This adds a receptor keyword argument to
Executing. On COPY FROM, receptor must be an iterable that gives the data to be
copied. On COPY TO, receptor must be a callable that receives contents of the
CopyData messages received(differs from Querying's receptor). If a receptor
isn't given, no information will be supplied for COPY FROM and Executing_tuples
will hold the information received on COPY TO.

Additionally, make some of the compound transactions more consistent by taking
the portal name before the query name.

Modified Files:
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pq/src:
client3.py (r1.6 -> r1.7)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/pq/src/client3.py.diff?r1=1.6&r2=1.7)