Transaction status in default psql prompt?

What do people think about adding the transaction status indicator to the
default psql prompt, so it'd look something like this:

peter=# begin;
BEGIN
peter*=# foo;
ERROR: syntax error at or near "foo" at character 1
peter!=# rollback;
ROLLBACK
peter=#

I think many people would find that useful.

Btw., would anyone mind if the code for this indicator where not %T, but
say instead %x, because there is a correspondence between psql's codes and
tcsh's, and tcsh uses %T for the hour of the day, which is something that
someone might want to add someday.

--
Peter Eisentraut peter_e(at)gmx(dot)net