[PATCH] Space reservation v02

I attached second version of space reservation patch. You can see first
version here:
http://archives.postgresql.org/pgsql-hackers/2008-12/msg00886.php

I thought about Heikki'es comments and I removed all catalog changes,
because there are not necessary to be in pg_class. Instead of
pg_preugrade script should create own schema (pg_upgrade) and tables on
its needs.

This patch implement settings like relation options. Tom had objection
about this approach. I can rewrite it and extend pg_class instead.
However before I will do it I would like to know opinion about rest of
the patch.

And last thing is most important. Space reservation MUST TO be implemented if we
want to have 8.4->8.5 upgrade. Else we will be at the begging...

Zdenek