Update existing bdr triggers to 'tgisinternal'

Update existing bdr triggers to 'tgisinternal'

New truncate_triggers are created as `tgisinternal` but
exiting ones are not changed. Fix that by doing a one-off
catalog update during the BDR extension upgrade, setting
any existing BDR truncate triggers to internal and appending
their oid to their names to match new triggers.

Further improvement for issue #62