pg_dump support for Extension, patch version 24

Hi,

Please find an updated (merged) version 24 of the extension patch set,
simplified to follow on Tom's comment about dependency tracking when
doing ALTER EXTENSION SET SCHEMA. We now follow only one level of
dependencies, and that just works (thanks Tom).

On the same idea, I also removed the pg_extension_objects() function and
implemented \dx+ using Alvaro's recent addition, pg_describe_object().
You can see this in the doc part of the incremental UPGRADE patch:

-SELECT 'alter ' || objdesc || ' set extension pair;'
- FROM pg_extension_objects('pair');
+SELECT 'alter ' || pg_describe_object(classid, objid, 0) || ' set extension pair;'
+ FROM pg_depend
+ WHERE refclassid = 'pg_extension'::regclass
+ AND refobjid = (SELECT oid FROM pg_extension WHERE extname = 'pair')

If some of you here had been working on the previous version of the
patch, the incremental diff is available on the git repository:

http://git.postgresql.org/gitweb?p=postgresql-extension.git;a=commitdiff;h=bac353f1040465b7bd95afbca2fd699f3bd699ff

Hey, look at that, an incremental patch that (again) removes code:
9 files changed, 53 insertions(+), 161 deletions(-)

The documentation is updated online too:

http://pgsql.tapoueh.org/extensions/doc/html/extend-extension.html

You will find 3 attachments related to the main extension's patch, the
all-inclusive patch, and the contrib and "core" separated out: Robert
said it could ease reviewing and git offers an easy way to do that
splitting. Also, please note that the ALTER EXTENSION UPGRADE patch is
incremental, you need to first apply the extension's patch.

Should an all-inclusive (Extension + Upgrade) patch suit some reviewer
here, just ask and I'll provide it, or you could git clone my repository.

Regards,
--
Dimitri Fontaine
http://2ndQuadrant.fr PostgreSQL : Expertise, Formation et Support