[FIX] registry: missing a threading.RLock in RegistryManager.get():

[FIX] registry: missing a threading.RLock in RegistryManager.get():

if no registry exists and several calls to RegistryManager.get() are called at the same time
by several threads, several registries will be created one after the other and only the last
one will be kept in cls.registries (courtesy of Guewen Baconnier (Camptocamp)

Invert behaviour of commit 3685 because, at that time, the new trigger the schedule_cron_jobs method which ran another lock and called get on the registry. We had a deadlock with the cron. This is no longer the case as we don't call the same method at the end of the creation of the registry and it does not trigger a lock

bzr revid: mat@openerp.com-20131114144401-k00podawlem7cjd1