python - pq: Add BindingsAndExecutings transaction.

Log Message:
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Add BindingsAndExecutings transaction. This provides a substantial optimization
for mass insertions. In addition, add the concept of non-fatal exceptions.
Exceptions in a transaction are meant to be fatal to the connection. However,
for BindingsAndExecutings and one other, when the receptor specifies an iterator
to push, it must execute out-of-transaction code that can raise an exception.
These exceptions can be safely caught without a connection fatality, so store it
in 'nf_exc_info' for later use/raising.

Modified Files:
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    pq/src:
        client3.py (r1.8 -> r1.9)
        (http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/pq/src/client3.py.diff?r1=1.8&r2=1.9)