pgsql: Change shell syntax that seems not to work right on FreeBSD

Log Message:
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Change shell syntax that seems not to work right on FreeBSD 6-CURRENT
buildfarm machines.

Modified Files:
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pgsql/src/test/regress:
pg_regress.sh (r1.55 -> r1.56)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/pg_regress.sh.diff?r1=1.55&r2=1.56)