Support explicit placement of the temporary-table schema within search_path, and disable searching it for functions and operators (Tom)

This is needed to allow a security-definer function to set a truly secure value of search_path. Without it, an unprivileged SQL user can use temporary objects to execute code with the privileges of the security-definer function (CVE-2007-2138). See CREATE FUNCTION for more information.

Fix potential-data-corruption bug in how VACUUM FULL handles UPDATE chains (Tom, Pavan Deolasee)