pgsql: Avoid bzero/bxopy in favor of more standard library routines.

Log Message:
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Avoid bzero/bxopy in favor of more standard library routines.
Marko Kreen

Modified Files:
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pgsql/contrib/pgcrypto:
sha2.c (r1.2 -> r1.3)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/pgcrypto/sha2.c.diff?r1=1.2&r2=1.3)