pg_upgrade and regclass

In Postgres 8.4, pg_upgrade preserved pg_class relfilenodes by creating
files in the file system.  In Postgres 9.0, we changed this by creating
pg_upgrade_support functions which allow us to directly preserve
pg_class.oids. 

Unfortunately, check.c was not updated to reflect this and clusters
using regclass were prevented from being upgraded by pg_upgrade.

I have developed the attached patch to allow clusters using regclass to
be upgraded.  I plan to apply it to PG 9.0, 9.1, and HEAD.

-- 
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + It's impossible for everything to be true. +