Clearing out old idle connections

Hullo :)

We have pg 8.1.3 and for whatever reason (network blips, poor pooling on
behalf of the client, etc.) we sometimes see a large number (dozens) of
old connections in the idle state which never get reused.

Is there a function in postgres similar to MySQL's 'wait_timeout' which
automatically closes any connections which have been idle for N seconds?
Is this functionality possible to to script/cron by examining the pg
catalogs and finding a 'last used' timestamp?

I am aware the correct response is 'deal with the cause, not the
symptoms', however I assure you that this academic approach wins no
friends in the enterprise market that postgres pitches itself at :)

Cheers,
Gavin.