backport stable branch and some vreg cleanups:
* move initialization_completed from cwvreg to base VRegistry class
allowing simplification of CWVregistry
* cleanup initialization process: __registered__ is now called after
initialization completed, by the relevant registry.
* fix/remove deprecated tests
from logilab.common.deprecation import class_renamed, class_moved
from cubicweb.server import hook
SystemHook = class_renamed('SystemHook', hook.Hook)
PropagateSubjectRelationHook = class_renamed('PropagateSubjectRelationHook',
hook.PropagateSubjectRelationHook)
PropagateSubjectRelationAddHook = class_renamed('PropagateSubjectRelationAddHook',
hook.PropagateSubjectRelationAddHook)
PropagateSubjectRelationDelHook = class_renamed('PropagateSubjectRelationDelHook',
hook.PropagateSubjectRelationDelHook)
Hook = class_moved(hook.Hook)