BUG #1219: pgxs does not work fully

The following bug has been logged online:

Bug reference:      1219
Logged by:          Fabien COELHO

Email address:      coelho@cri.ensmp.fr

PostgreSQL version: 8.0 Beta

Operating system:   Linux debian

Description:        pgxs does not work fully

Details:

When testing the pgxs framework with various contribs,
some (at least pgbench) do not compile because:

(1) missing file: libpgport.*

(2) non adapted macros: libpq_*dir

(3) testing the feature is not easy because
    the makefiles in contrib do not allow to use it,
    so one has to fix the makefiles first.

Moreover I really think that even if Peter finds it useless it should be
allowed to use pgxs for contribs
especially as it may be useful to others and as it
does not necessarily harm.

I'm planing to submit yet another patch so as to fix
this again while still preserving the vpath behavior.