pgsql: Print out diff status code when we think there's a hard failure.

Log Message:
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Print out diff status code when we think there's a hard failure.
May help in debugging behavior on Windows.

Modified Files:
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pgsql/src/test/regress:
pg_regress.c (r1.8 -> r1.9)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/pg_regress.c.diff?r1=1.8&r2=1.9)