Fix string/bytes issues under python 3. 1) cgi/client.py: override cgi.FieldStorage's make_file so that file is always created in binary/byte mode. This means that json (and xml) are bytes not strings. 2) rest.py: try harder to find dicttoxml in roundup directory or on sys.path. This just worked under python 2 but python 3 only searches sys.path by default and does not search relative like python 2. 3) rest.py: replace headers.getheader call removed from python 3 with equivalent code. 4) rest.py: make value returned from dispatch into bytes not string. 5) test/caseinsensitivedict.py, test/test_CaseInsensitiveDict.py: get code from stackoverflow that implements a case insensitive key dict. So dict['foo'], dict['Foo'] are the same entry. Used for looking up headers in mocked http rewuset header array. 6) test/rest_common.py: rework tests for etags and rest to properly supply bytes to the called routines. Calls to s2b and b2s and use of BytesIO and overriding make_file in cgi.FieldStorage to try to make sure it works under python 3.

--- a/roundup/cgi/client.py	Sun Mar 17 19:00:43 2019 -0400
+++ b/roundup/cgi/client.py	Sun Mar 17 19:28:26 2019 -0400
@@ -375,7 +375,18 @@
                     logger.debug("Setting CONTENT_LENGTH to 0 for method: %s",
                                 self.env['REQUEST_METHOD'])
 
+            # cgi.FieldStorage must save all data as
+            # binary/bytes. This is needed for handling json and xml
+            # data blobs under python 3. Under python 2, str and binary
+            # are interchangable, not so under 3.
+            def make_file(self):
+                import tempfile
+                return tempfile.TemporaryFile("wb+")
+
+            saved_make_file = cgi.FieldStorage.make_file
+            cgi.FieldStorage.make_file = make_file
             self.form = cgi.FieldStorage(fp=request.rfile, environ=env)
+            cgi.FieldStorage.make_file = saved_make_file
             # In some case (e.g. content-type application/xml), cgi
             # will not parse anything. Fake a list property in this case
             if self.form.list is None: