python - ip: Set GTX as a builtin instead of filling it in as a local.

Log Message:
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Set GTX as a builtin instead of filling it in as a local.

While it would be preferrable not to touch the builtins module, having GTX
there seems most appropriate. Having it as it was before makes '-m module' less
useful as access to the connection is hidden by the module layer. Having it
available through an import statement seems unnatural as it is a single
connection object, not a module.

Also, add the -X option for wrapping the entire run in a transaction block.
Whether xact or subxact being implementation dependent.

Modified Files:
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    ip/src:
        python.py (r1.2 -> r1.3)
        (http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/ip/src/python.py.diff?r1=1.2&r2=1.3)