[PATCH] Largeobject Access Controls (r2432)

The attached patch is a revised version of large object privileges
based on the feedbacks at the last commit fest.

List of updates:
* Rebased to the latest CVS HEAD
* Add pg_largeobject_aclcheck_snapshot() interface.
In the read-only access mode, large object feature uses
query's snaphot, not only SnapshotNow. This behavior also
should be applied on accesses to its metadata.
When it makes its access control decision, it has to fetch
database acls from the system catalog. In this time, we scan
the pg_largeobject_metadata with a snapshot of large object
descriptor. (Note that it is SnapshotNow in read-write mode.)
It enables to resolve the matter when access rights are changed
during large objects are opened.
* Add pg_dump support.
* Replace all the "largeobject" by "large object" from
user visible messages and documentation.
* Remove ac_largeobject_*() routines because we decided
not to share same entry points between DAC and MAC.
* Add a description of large object privileges in SGML.
* Add a definition of pg_largeobject_metadata in SGML.
* \lo_list command supports both of v8.5 and prior version.

Thanks,
--
OSS Platform Development Division, NEC
KaiGai Kohei <kaigai(at)ak(dot)jp(dot)nec(dot)com>