Include recipe for updating pg_aggregate to fix avg(money) function.

migration/6.2_to_6.2.1

@@ -4,3 +4,11 @@ but is required from any release prior to v6.2.
 In upgrading from v6.2, if you choose to dump/reload you will find that
 avg(money) is now calculated correctly. All other bug fixes take effect
 upon updating the executables.
+
+Another way to avoid dump/reload is to use the following SQL command
+from psql to update the existing system table:
+
+  update pg_aggregate set aggfinalfn = 'cash_div_flt8'
+   where aggname = 'avg' and aggbasetype = 790;
+
+This will need to be done to every existing database, including template1.