'Actually check if the mutated URL exists.
:return: None, all important data is put() to self.output_queue'

def _check_existance(self, original_response, mutant):

    response = self._uri_opener.send_mutant(mutant)
    if is_404(response):
        return
    if fuzzy_not_equal(original_response.body, response.body, 0.85):
        rand = rand_alpha()
        rand_mutant = mutant.copy()
        rand_mutant.set_token_value(rand)
        rand_response = self._uri_opener.send_mutant(rand_mutant)
        if fuzzy_not_equal(response.body, rand_response.body, 0.85):
            fr = FuzzableRequest(response.get_uri())
            self.output_queue.put(fr)
