pgsql: As a stopgap to get the Windows buildfarm members running again,

Log Message:
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As a stopgap to get the Windows buildfarm members running again, hot-wire
the check on diff's exit status to check for literally 0 or 1.  Someone
should look into why WIFEXITED/WEXITSTATUS don't work for this, but I've
spent more than enough time on it already.

Modified Files:
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    pgsql/src/test/regress:
        pg_regress.c (r1.9 -> r1.10)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/pg_regress.c.diff?r1=1.9&r2=1.10)