cleanup of pgsql_tmp directory

This morning we found out that our filesystem was at 98% and filling
quickly. We immediately found one query running for a long time and saw
1500+ files in the pgsql_tmp directory we could attribute to it.

I killed using pg_terminate_backend and some space was reclaimed, but the
temporary files from the process are still in the pgsql_tmp directory.

We're on postgres 8.4.9 on centos. Which process should be deleting these
files and what is normally the delay? I'm assuming the postmaster process
will eventually delete them, but does the server have to be bounced in order
for this to happen? It's been 30 minutes since the process was killed.

Also, is there some method of governing the temporary space used? Our
temp_tablespace parameter is null.

Thanks

Robert