No index support for date/time types?

I'm getting some strange errors when trying to use a btree (default) index
on any of timestamp, abstime, datetime, or reltime types.  All fail with an
error:

(timestamp)  ERROR:  Can't find a default operator class for type 1296.
(abstime)  ERROR:  Cannot create index: attribute 11 does not exist
(reltime)  ERROR:  Can't find a default operator class for type 703.
(datetime)  ERROR:  Cannot create index: attribute 12 does not exist

...errors which, of course, mean nothing to me.  8-)

A simple case to reproduce the first ...

create table foo (bar timestamp);
create index baz on foo (bar);

--
-- Todd Vierling (tv@pobox.com)