[FIX] ir.model: during garbage collection of obsolete records in _process_end,...

[FIX] ir.model: during garbage collection of obsolete records in _process_end, do it in anti-chronological order

Just like for the uninstallation process, records should be
deleted with last created first, as an attempt to reverse
the operations in the right order (to avoid errors due to
dependencies between records).

bzr revid: odo@openerp.com-20131118125640-kdo3t34uszqggu13