[testlib] simple helper method to register temporary appobjects (hooks for instance) with a context manager

[undo] fix transactions table name in cleanup operation

Add context management methode to dbapi.Connection the connection is automaticly closed when exiting the context.

i18n update

[i18n] use named substitution to avoid gettext warnings

[dataimport] print transaction id when we get one

[cleanup] add some notes

[optimisation] _select_best is used very intensivly. Peanuts optimization may count :)

[optimization] traced_selection is used very intensively in debug mode optimizing it is worth the pain. Basically : don't do stuff unnecessary when we don't trace anything.

[optimization] improve massive write performance by optimizing hooks selection profiling on some massive deletion showed up that 2/3 of the time was spent in hooks selection. Those changes make it much more acceptable (through selection is still not negligeable): * use one registry for each event, so we've much less hooks to check when emiting an event as well as no more need for the match_event selector. This required ability to put one appobject into several registries, using a __registries__ class attribute. * check for deprecated .enabled at registry initialization time instead of at selection time A very simple HooksManager class has been reintroduce to choose the right registry on call_hooks. Those optimisations leads to a ~x3 factor of time necessary to delete 16000 entities.