symmetry with regprocout.

what is_opclause will accept.

A test case is:
create table linetab (x line);
select * from linetab where ?| x;
which coredumps in 6.4.2 and current sources.

 decade, century, or millenium.

Fix problem with date_part() for timespan (had an offset of one)
 when given decade, century, and millenium as arguments.
 Reported by Ricardo J.C.Coelho.

Change #if FALSE to #if NOT_USED to avoid port problems.
Fix up pg_indent weirdness with function argument declarations.

Fix output type for int8out, but I don't think it matters.

 modules. Used to be in dt.c I think.