IMHO, using a fileno property looks better than __getattr__. Setting an
attribute in init works too, unless fp changes during the object life
(then 3.x is broken IIUC).

It works OK as a property of either urllib.addinfourl or of
httplib.HTTPResponse (socket would work, but is this broken there or a
higher layer). 

Tests and fixes for both solutions attached. As soon as one is chosen,
some docs on fileno would be nice, even for 3.x.


This (current) test in test_urllibnet.py passes, but I don't see how to
improve it, assuming it should fail/detect this bug (maybe self.urlopen
isn't testing urllib.urlopen correctly?):

    def test_fileno(self):
        if (sys.platform in ('win32',) or
                not hasattr(os, 'fdopen')):
            # On Windows, socket handles are not file descriptors; this
            # test can't pass on Windows.
            return
        # Make sure fd returned by fileno is valid.
        open_url = self.urlopen("http://www.python.org/")
        fd = open_url.fileno()
        FILE = os.fdopen(fd)