CMFActivity: Always set zope.globalrequest WIP

ERP5 uses a mix of context.REQUEST and Products.ERP5Type.Global.get_request(),
which now uses zope.globalrequest.getRequest().
CMFActivity reconstruct the original request before executing activity, so that
the activity is executed with a request equivalent to the request at the time
where the method was activated. For this, context.REQUEST was properly restored,
but get_request()/globalrequest was only restored when the REQUEST had some
ACCEPT_LANGUAGE header, so that it replays the language negociation for
Localizer.
With browser requests, I guess every browser pass an ACCEPT_LANGUAGE header,
but within unit tests such header is not present.

(TODO: finish this message)