date math: converting interval result to seconds

hi-

i'm trying to do something like this:

triv=> SELECT current_timestamp-stime as tm FROM triv_a_r WHERE tq_id =
'QM7DGLU15' AND fid_c = 'PTA42BEAE';
          tm
-----------------------
 2 days 18:32:46.06146
(1 row)


but i'd like the resulting interval to be represented in seconds.  i've
looked through the various date functions in the docs (date_part,
date_trunc, extract), and none of them seem to do this.  are there any
such date conversion functions?

i'm using 7.2.1 on solaris 8.

thanks-

dan