python - fe: PStatement refactor, Transaction with, and more interrupt

Log Message:
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PStatement refactor, Transaction with, and more interrupt support.

Refactor PreparedStatement into two classes, the base PreparedStatement and the
ClientPreparedStatement. The difference lies in ClientPreparedStatement's
ability to re-prepare itself, and in its need to close itself on delete due to
the statement_id's id() based generation.
Similarly, for Portal's __del__ method, close if unclosed and ID(self) =
portal_id.

Fix with-statement support in Transaction.

Don't close pipes on __del__(We don't know if we're actually done with the
pipe's resources--ie the fd) and initialize the interrupt attribute to False.
(.interrupt is used to signal the read loop to raise an OperationInterrupt
exception)

Modified Files:
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fe/src:
tracenull.py (r1.29 -> r1.30)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/fe/src/tracenull.py.diff?r1=1.29&r2=1.30)
transport.py (r1.3 -> r1.4)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/fe/src/transport.py.diff?r1=1.3&r2=1.4)
fe/test:
tracenull.py (r1.16 -> r1.17)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/fe/test/tracenull.py.diff?r1=1.16&r2=1.17)

Removed Files:
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fe/test:
dbapi2.py
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/fe/test/dbapi2.py)