currval and DISCARD ALL

Hi,
is there a way to clear the session state of sequence values fetched by
currval(regclass)? "DISCARD ALL" doesn't seem to do it.

eg. (w/ pg 9.2.4)
test=# CREATE SEQUENCE foo_seq;
CREATE SEQUENCE
test=# SELECT nextval('foo_seq');
-[ RECORD 1 ]
nextval | 1

test=# SELECT currval('foo_seq');
-[ RECORD 1 ]
currval | 1

test=# DISCARD ALL;
DISCARD ALL
test=# SELECT currval('foo_seq');
-[ RECORD 1 ]
currval | 1

I'm trying to migrate a large web app to work with pgbouncer's
transaction pool mode and it would be easier to identify issues if
currval() would return the usual "ERROR: currval of sequence "foo_seq"
is not yet defined in this session" if nextval() wasn't called in the
same pgbouncer session instead of getting old numbers from past
transactions.

thanks,
-nigel.