interceptor (Needle::ServicePoint)

    # File lib/needle/service-point.rb, line 89
        def interceptor( interceptor )
          @element_mutex.synchronize do
            element = @pipeline.get( :interceptor )
            unless element
              @pipeline.add( :interceptor )
              element = @pipeline.get( :interceptor )
            end
            element.interceptors << interceptor
            @pipeline.reset!
            @chain = nil
          end
        end