Pg_upgrade and collation

The attached patch documents that pg_upgrade requires old/new servers to
use compatibile collation library versions as well.

I would like to apply this to all PG branches.

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

+ As you are, so once was I. As I am, so you will be. +
+                     Ancient Roman grave inscription +