pgsql: Prevent multiple archivers from starting.

Log Message:
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Prevent multiple archivers from starting. Backpatch to 8.1.X.

Simon Riggs

Tags:
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REL8_1_STABLE

Modified Files:
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pgsql/src/backend/catalog:
pg_conversion.c (r1.28 -> r1.28.2.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/catalog/pg_conversion.c.diff?r1=1.28&r2=1.28.2.1)
pgsql/src/backend/postmaster:
pgarch.c (r1.18 -> r1.18.2.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/postmaster/pgarch.c.diff?r1=1.18&r2=1.18.2.1)