Extend ALTER DEFAULT PRIVILEGES for large objects

Hi,

Currently, ALTER DEFAULT PRIVILEGE doesn't support large objects,
so if we want to allow users other than the owner to use the large
object, we need to grant a privilege on it every time a large object
is created. One of our clients feels that this is annoying, so I would
like propose to extend  ALTER DEFAULT PRIVILEGE to large objects. 

Here are the new actions allowed in abbreviated_grant_or_revoke;

+GRANT { { SELECT | UPDATE }
+    [, ...] | ALL [ PRIVILEGES ] }
+    ON LARGE OBJECTS
+    TO { [ GROUP ] role_name | PUBLIC } [, ...] [ WITH GRANT OPTION ]

+REVOKE [ GRANT OPTION FOR ]
+    { { SELECT | UPDATE }
+    [, ...] | ALL [ PRIVILEGES ] }
+    ON LARGE OBJECTS
+    FROM { [ GROUP ] role_name | PUBLIC } [, ...]
+    [ CASCADE | RESTRICT ]

A new keyword OBJECTS is introduced for using plural form in the syntax
as other supported objects. A schema name is not allowed to be specified
for large objects since any large objects don't belong to a schema.

The attached patch is originally proposed by Haruka Takatsuka
and some fixes and tests are made by me. 

Regards,
Yugo Nagata

-- 
Yugo NAGATA <nagata@sraoss.co.jp>