get_whatever_oid, part 1: object types with unqualifed names

Link to previous discussion:

http://archives.postgresql.org/pgsql-hackers/2010-05/msg01195.php

Attached, please find a patch which standardizes the following
interface for object types that use unqualifed names.

Oid get_whatever_oid(char *name, bool missing_ok);

It also refactors the existing code to use these functions whenever
possible.  I'm going to work up a similar path for the object types
that use qualified names, but I thought it would be a good idea to
send this first before I invest too much time in it.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise Postgres Company