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.

import operator

class MultiMapping:
    def __init__(self, *stores):
        self.stores = list(stores)
    def __getitem__(self, key):
        for store in self.stores:
            if key in store:
                return store[key]
        raise KeyError(key)
    _marker = []
    def get(self, key, default=_marker):
        for store in self.stores:
            if key in store:
                return store[key]
        if default is self._marker:
            raise KeyError(key)
        return default
    def __len__(self):
        return sum([len(x) for x in self.stores])
    def push(self, store):
        self.stores.append(store)
    def pop(self):
        return self.stores.pop()
    def items(self):
        l = []
        for store in self.stores:
            l = l + list(store.items())
        return l