varchar_pattern_ops in 7.3.4?

I'd like to be able to do queries like "select count(*), fromline from
message where subject like 'Couldn%'" quickly.  I see that, in current
Postgres, I can do this with an index like "create index message_subject
on message using btree(subject varchar_pattern_ops)".  But I'm using
Postgres 7.3.4, and it doesn't seem to have varchar_pattern_ops in its
pg_opclass.opcname.  Is there an easier way to do these queries than
upgrading?