bpo-29979: Rewrite cgi.parse_multipart to make it consistent with FieldStorage (#991)

diff --git a/Lib/test/test_cgi.py b/Lib/test/test_cgi.py
index 6373221..903d073 100644
--- a/Lib/test/test_cgi.py
+++ b/Lib/test/test_cgi.py
@@ -126,8 +126,8 @@
         env = {'boundary': BOUNDARY.encode('latin1'),
                'CONTENT-LENGTH': '558'}
         result = cgi.parse_multipart(fp, env)
-        expected = {'submit': [b' Add '], 'id': [b'1234'],
-                    'file': [b'Testing 123.\n'], 'title': [b'']}
+        expected = {'submit': [' Add '], 'id': ['1234'],
+                    'file': [b'Testing 123.\n'], 'title': ['']}
         self.assertEqual(result, expected)
 
     def test_fieldstorage_properties(self):