Those "properties" were put in _threads_dict (cf __setattr__), but only for
the thread who instantiates ThreadContext (until next "clear" call from/for
that thread, where they are not inserted in cleared version).

git-svn-id: https://svn.erp5.org/repos/neo/trunk@1787 71dcc9de-d417-0410-9af5-da40c76e7ee4