Fix for pg_upgrade

The attached patches fixes a pg_upgrade crash in 9.0 caused by a new
cluster database that doesn't exist in the old cluster;  instead throw
an error.  This was reported to me by EnterpriseDB testing staff.  This
bug does not exist in git head.

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

  + It's impossible for everything to be true. +
diff --git a/contrib/pg_upgrade/relfilenode.c b/contrib/pg_upgrade/relfilenode.c
new file mode 100644
index b20ca20..fc36968
*** a/contrib/pg_upgrade/relfilenode.c
--- b/contrib/pg_upgrade/relfilenode.c
*************** transfer_all_new_dbs(migratorContext *ct
*** 46,51 ****
--- 46,55 ----
          int            n_maps;
          pageCnvCtx *pageConverter = NULL;

+         if (!old_db)
+             pg_log(ctx, PG_FATAL,
+                "the new cluster database %s was not found in the old cluster\n", new_db->db_name);
+
          n_maps = 0;
          mappings = gen_db_file_maps(ctx, old_db, new_db, &n_maps, old_pgdata,
                                      new_pgdata);