python - fe: Extend testCopy and testCopyFail.

Log Message:
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Extend testCopy and testCopyFail.

This now checks empty, single, and double copy sets. Also, make it copy the
data back out, and compare it against what was sent in.
Make testCopyFail validate that the transaction state is in error after the
CopyFail was sent. (Check immediate and after-one failures)

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