Merge branch 'develop' into key_val_lists

diff --cc requests/models.py
Simple merge

diff --cc tests/test_requests.py
index 076ca6c,9204b15..6fe0d75
--- 1/tests/test_requests.py
--- 2/tests/test_requests.py
+++ b/tests/test_requests.py
@@@ -1024,10 -972,13 +1024,17 @@@ class RequestsTestSuite(TestSetup, Test
          t = json.loads(r.text)
          self.assertEqual(t.get('form'), {'field': 'a, b'})
          self.assertEqual(t.get('files'), files)
 +        r = post(httpbin('post'), data=data, files=files.items())
 +        t = r.json
 +        self.assertEqual(t.get('form'), {'field': 'a, b'})
 +        self.assertEqual(t.get('files'), files)
  
+     def test_str_data_content_type(self):
+         data = 'test string data'
+         r = post(httpbin('post'), data=data)
+         t = json.loads(r.text)
+         self.assertEqual(t.get('headers').get('Content-Type'), '')
+ 
+ 
  if __name__ == '__main__':
      unittest.main()