Patch: regschema OID type

Hey -hackers,

Enclosed is a patch adding a 'regschema' OID type.  I'm really just  
hoping to get this out there, don't worry about committing it at this  
point.  This is something that I've always wanted in the field (yes,  
I'm lazy).  Many thanks to RhodiumToad for pointers about the  
necessary system table entries and general advice.

Example usage:

machack:postgres:8555=# select relnamespace::regschema, relname from  
pg_class limit 10;
     relnamespace    |           relname
--------------------+------------------------------
  pg_catalog         | pg_type
  pg_catalog         | pg_attribute
  information_schema | foreign_data_wrapper_options
  information_schema | foreign_data_wrappers
  information_schema | _pg_foreign_servers
  information_schema | foreign_server_options
  information_schema | foreign_servers
  information_schema | _pg_user_mappings
  information_schema | user_mapping_options
  information_schema | user_mappings
(10 rows)

It uses the same quoting mechanism as regclass, and I've tested  
against some odd schema names such as "foo""schema"; I updated the  
docs as I was able, but am not familiar enough with the regression  
tests to add those yet.  I hope to address that in a future revision.

Thanks,

David
--
David Christensen
End Point Corporation
david@endpoint.com