title: Requests stops when multiple requests sent in a row
body: <p>I'm parsing online shops using scrapy and python-requests, and after i get all the info i'm making one more request to get qty by python-requests, and after several minutes spider stops working
  I dont know what is causing the trouble. Any suggestions?</p>
  
  <p>Scrapy Log:</p>
  
  <pre><code>2014-05-08 15:27:57+0300 [scrapy] DEBUG: Start adding sku1270594 to a cart.
  INFO:requests.packages.urllib3.connectionpool:Starting new HTTP connection (1): www.sds.com.au
  DEBUG:requests.packages.urllib3.connectionpool:"GET /product/trefoil-tee-by-adidas-in-black-camo-grey HTTP/1.1" 200 20223
  INFO:requests.packages.urllib3.connectionpool:Starting new HTTP connection (1): www.sds.com.au
  DEBUG:requests.packages.urllib3.connectionpool:"POST /common/ajaxResponse.jsp;jsessionid=34E95C7662D0F5084FF971CC5693E6E8.store-node1?_DARGS=/browse/product.jsp.addToCartForm HTTP/1.1" 200 146
  2014-05-08 15:27:59+0300 [scrapy] DEBUG: End adding sku1270594 to a cart.
  2014-05-08 15:27:59+0300 [scrapy] DEBUG: Success. quantity of sku1270594 is 16.
  2014-05-08 15:28:00+0300 [sds] DEBUG: Updating  product info sku1270594
  2014-05-08 15:28:00+0300 [sds] DEBUG: Added new price sku1270594
  2014-05-08 15:28:00+0300 [sds] DEBUG: Scraped from &lt;200 http://www.sds.com.au/product/trefoil-tee-by-adidas-in-black-camo-grey&gt;
  2014-05-08 15:28:00+0300 [sds] DEBUG: Updating  product info sku901159
  2014-05-08 15:28:00+0300 [sds] DEBUG: Added new price sku901159
  2014-05-08 15:28:00+0300 [sds] DEBUG: Scraped from &lt;200 http://www.sds.com.au/product/two-palm-tee-by-folke-in-chalk&gt;
  2014-05-08 15:28:00+0300 [sds] DEBUG: Updating  product info sku901163
  2014-05-08 15:28:00+0300 [sds] DEBUG: Added new price sku901163
  2014-05-08 15:28:00+0300 [sds] DEBUG: Scraped from &lt;200 http://www.sds.com.au/product/two-palm-tee-by-folke-in-chalk&gt;
  2014-05-08 15:28:00+0300 [scrapy] DEBUG: Start adding sku1270591 to a cart.
  INFO:requests.packages.urllib3.connectionpool:Starting new HTTP connection (1): www.sds.com.au
  DEBUG:requests.packages.urllib3.connectionpool:"GET /product/trefoil-tee-by-adidas-in-black-camo-grey HTTP/1.1" 200 20225
  INFO:requests.packages.urllib3.connectionpool:Starting new HTTP connection (1): www.sds.com.au
  </code></pre>
  
  <p>And that's it.Nothing happens in console anymore.
  Here's the function that gets the quantity:</p>
  
  <pre><code>def get_qty(self, item):
      r = requests.get(item['url'])
      cookie_cart_user = dict(r.cookies)
      sel = Selector(text=r.text, type="html")
      session = sel.xpath('//input[@name="_dynSessConf"]/@value').extract()[0]
      # print session
      # print cookie_cart_user
      add_to_cart_url = 'http://www.sds.com.au/common/ajaxResponse.jsp;jsessionid=%s?_DARGS=/browse/product.jsp.addToCartForm' % cookie_cart_user['JSESSIONID']
      # ok, so we're adding one item
      log.msg("Adding %s to a cart." % item['internal_id'], log.DEBUG)
      headers = {
          'User-Agent': USER_AGENT,
          'Accept': 'application/json, text/javascript, */*; q=0.01',
          'Connection': 'close',
      }
      s = requests.session()
      s.keep_alive = False
      r = requests.post(add_to_cart_url,
                        data=self.generate_form_data(item, 10000, session),
                        cookies=cookie_cart_user,
                        headers=headers,
                        timeout=10)
      response = r.json()
      r.close()
      try:
          quantity = int(re.findall(u'\d+', response['formErrors'][0]['errorMessage'])[0])
          log.msg("Success. quantity of %s is %s." % (item['internal_id'], quantity), log.DEBUG)
          return quantity
      except Exception, e:
          log.msg('Error getting data-cart-item on product %s. Error: %s' % (item['internal_id'], str(e)), log.ERROR)
          with open("log/%s.html" % item['internal_id'], "w") as myfile:
              myfile.write('%s' % r.text.encode('utf-8'))
  </code></pre>