python - be: Append traceback information to detail if it is a Postgres

Log Message:
-----------
Append traceback information to detail if it is a Postgres error, rather than
leaving the traceback out.

Remove some dead code, and other minor touch-ups.

Modified Files:
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be/src:
pl.c (r1.5 -> r1.6)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/be/src/pl.c.diff?r1=1.5&r2=1.6)