[IMP] core: manage registries via an LRU.

When working with a large number of databases, the memory allocated to
registries wasn't limited, resulting to waste memory (especially in the
longpolling worker, which is not recycled).
The size of the LRU is depending on the soft limit configured for
workers.
[FIX] l10n_fr: "passif" part of the "bilan" report

Report's model was full, but not the view. Leftover of rev 7e8dcc5600b61d68af
refactoring.
Merge branch '8.0' of https://github.com/odoo/odoo into 8.0-linux64