Mention pg_upgrade sets autovacuum_freeze_max_age to maximum.

contrib/pg_upgrade/server.c

@@ -172,8 +172,8 @@ start_postmaster(ClusterInfo *cluster, bool quiet)
 	 *
 	 * Using autovacuum=off disables cleanup vacuum and analyze, but
 	 * freeze vacuums can still happen, so we set
-	 * autovacuum_freeze_max_age very high.  We assume all datfrozenxid and
-	 * relfrozen values are less than a gap of 2000000000 from the current
+	 * autovacuum_freeze_max_age to its maximum.  We assume all datfrozenxid
+	 * and relfrozen values are less than a gap of 2000000000 from the current
 	 * xid counter, so autovacuum will not touch them.
 	 */	
 	snprintf(cmd, sizeof(cmd),