pgsql: Document that Bucardo is an example of mulit-master replication

Log Message:
-----------
Document that Bucardo is an example of mulit-master replication with
conflict resolution.

Modified Files:
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pgsql/doc/src/sgml:
high-availability.sgml (r1.32 -> r1.33)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/high-availability.sgml?r1=1.32&r2=1.33)