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.

class StringFragmentCmpHelper:
    def compareStringFragments(self, s, fragments):
        """Compare a string agains a list of fragments where a tuple denotes a
        set of alternatives
        """
        pos = 0
        for frag in fragments:
            if type(frag) != tuple:
                self.assertEqual(s[pos:pos + len(frag)], frag)
                pos += len(frag)
            else:
                found = False
                for alt in frag:
                    if s[pos:pos + len(alt)] == alt:
                        pos += len(alt)
                        found = True
                        break

                if not found:
                    l = max(map(len, frag))
                    raise AssertionError('%s != %s' %
                                         (repr(s[pos:pos + l]), str(frag)))
        self.assertEqual(s[pos:], '')