[captcha] handle captcha validation properly in the captcha widget
also, avoid error if pil isn't installed (only a recommendation)
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)