new_contents: from __future__ import generator_stop
  
  
  
  from          : keyword.control.flow.python, source.python
                : source.python
  __future__    : source.python, support.variable.magic.python
                : source.python
  import        : keyword.control.import.python, source.python
                : source.python
  generator_stop : source.python
  
subject: Add a test for "from __future__ import .."