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.

''' Wrapper for getargspec to support other callables and python 3 support

In python 3 just uses getfullargspec which handles regular functions
and classes with __call__ methods.
'''

try:
    # Python 3+
    from inspect import getfullargspec as getargspec
    findargspec = getargspec
except:
    # Python 2.5-2.7 modified from https://bugs.python.org/issue20828
    import inspect

    def findargspec(fn):
        if inspect.isfunction(fn) or inspect.ismethod(fn):
            inspectable = fn
        elif inspect.isclass(fn):
            inspectable = fn.__init__
        elif hasattr(fn, '__call__'):
            inspectable = fn.__call__
        else:
            inspectable = fn

        try:
            return inspect.getargspec(inspectable)
        except TypeError:
            raise