navigation slot should be totally omit if there is no items in the context

[geohuz]

If there is no items in the context, we still get a blank "place holder" in the page, that is mostly we don't need. I add several lines in the Navigation class, like below:

class Navigation(object):

def __init__(self, context, request):
    self.context = context
    self.request = request
    self.location = 'top'
    self.slot = getattr(self.request, 'kotti_slot', None)

    # added by georgehu, to cancel the slot totally when we get a
    # empty list of items
    items = get_children(self.context, self.request, self.location)

    if self.slot is not None and items:
        self.location = self.slot

[j23d]

With these additions the tests will fail currently. Have to have a closer look.