BUG #3233: Trigger checks failed on concurrent transactions

The following bug has been logged online:

Bug reference:      3233
Logged by:          Dmitry Belyavsky
Email address:      beldmit@masterhost.ru
PostgreSQL version: 8.1.6
Operating system:   FreeBSD 6
Description:        Trigger checks failed on concurrent transactions
Details:

Greetings!

I have a table containing IP ranges and a BEFORE INSERT trigger checking the
ranges I insert don't intersect already existing ranges. So the concurrent
transactions are able to insert 2 intersecting ranges.

Whether TODO record "Allow statement-level triggers to access modified rows"
concerns the case I report?

Is there any workaround except LOCK TABLE causing performance degradation?

Thank you!