Turn autocommit off ?

Hi there !

It has now happened several times that I wanted to rollback some 
changes (like update, delete,...) I made to some tables. And since I
always forget to start a transaction, a simple ROLLBACK doesn't work
because of that quiet annoying autocommit in psql. 

I'd like to have automatically started a transaction which explicitly
must be termintated with commit or rollback.

Is there a way to turn autocommit off ? If not, perhaps it could
be a feature for the todo list ?

I'm currently using the cvs from last sunday on linux 2.1.119.

Thanks for any hints. 

Andreas