pgsql-server: Add documentation for pg_cancel_backend and

Log Message:
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Add documentation for pg_cancel_backend and pg_terminate_backend.

Magnus Hagander

Modified Files:
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pgsql-server/doc/src/sgml:
func.sgml (r1.209 -> r1.210)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/doc/src/sgml/func.sgml.diff?r1=1.209&r2=1.210)