Re: Extensions support for pg_dump, patch v27

I have gone ahead and committed the core and documentation parts of this
patch, but not as yet any of the contrib changes; that is, all the
contrib modules are still building old-style.  I had intended to do it
in two steps all along, so as to get some buildfarm proof for the thesis
that we haven't broken old-style add-on modules.  However, there is now
an additional motivation for delay: so long as we haven't pulled the
trigger on changing the contrib modules, this is an experimental feature
that nothing else depends on.  Worst case, if we can't get to a
satisfactory resolution of the pg_upgrade and ALTER EXTENSION UPGRADE
issues, we can ship 9.1 as-is and just label the EXTENSION commands as
subject to change.  I will however now go work on those issues.
        regards, tom lane