How best to load modules?

Hello, all!

What are best practices regarding the loading of postgresql modules, say
from the contrib/ directory; specifically, with regard to portability?

I would like to distribute an SQL script which loads a module, and works
with as little further fiddling as possible.

known options
=============

Within a session, or in a script, one can use
\i <explicit file path>
But within a script this has the weakness that the file path varies from
one system distribution to another.

One can start psql with
psql ... -f <explicit file path>
but that's a measure taken outside the script, to done either with session,
or else be done by a further measure such as a shell script.

Ideally, the location of the default modules directory (or installation
directory) should be available within a session in some variable or from
some function call.

There are some pre-defined variables, listed in a session by
show all;
but I don't see anything like a directory path there.
Maybe a built-in function returning this directory? Searched to no avail:
http://www.postgresql.org/docs/8.2/interactive/functions.html

There has been talk about a bigger solution on
http://wiki.postgresql.org/wiki/Module_Manager
but little seems to have happened there in some years.

An environment variable
$libdir,
is mentioned
http://www.postgresql.org/docs/8.2/static/runtime-config-client.html
but this seems not to be present within a session.
It seems to be expanded within the LANGUAGE C environment, for instance in
tablefunc.sql
-------------------------------------------------
CREATE OR REPLACE FUNCTION crosstab2(text)
RETURNS setof tablefunc_crosstab_2
AS '$libdir/tablefunc','crosstab'
LANGUAGE C STABLE STRICT;
-------------------------------------------------

Thanks!

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