bpo-20504 : in cgi.py, fix bug when a multipart/form-data request has… (#10638)

* bpo-20504 : in cgi.py, fix bug when a multipart/form-data request has no content-length header

* Add Misc/NEWS.d/next file.

* Add rst formatting for NEWS.d/next file

* Reaplce assert by self.assertEqual
3 files changed