title: gevents: 'TypeError: a float is required' error message when downloading files
body: <p>I'm trying to use gevents to download some images from the web. The images download but I get the following error which arrises when I'm joining the jobs. </p>
  
  <pre><code>pool.join(jobs)
  TypeError: a float is required
  </code></pre>
  
  <p>The images do download but I don't think I'm threading them correctly ... Would anyone know what I'm doing wrong..? </p>
  
  <pre><code>pool = Pool(3)
  N = 3
  
  urls = ['http://commons.wikimedia.org/wiki/File:Ultraviolet_image_of_the_Cygnus_Loop_Nebula_crop.jpg', 'http://commons.wikimedia.org/wiki/File:Ultraviolet_image_of_the_Cygnus_Loop_Nebula_crop.jpg,'http://commons.wikimedia.org/wiki/File:Ultraviolet_image_of_the_Cygnus_Loop_Nebula_crop.jpg'http://commons.wikimedia.org/wiki/File:Ultraviolet_image_of_the_Cygnus_Loop_Nebula_crop.jpg']
  
  finished = 0
  
  def download_file(url):
      global finished
  
      print('starting %s' % url)
      try:
          data = urllib2.urlopen(url, timeout=10000)
      except urllib2.URLError, e:
          print 'e : ' % e
      else:
          data = data.read()
          filename = os.path.basename(url)
          f = open(filename, 'wb')
      f.write(data)
      f.close()
      finally:
          finished += 1
  
  with gevent.Timeout(10000000, False):
      for x in xrange(10, 10 + N):
          jobs = [pool.spawn(download_file, url) for url in urls]
          pool.join(jobs)
  
  print('Finished %s' % (finished, N))
  </code></pre>