issue with IIS 6.5 or self-signed certificates (lp:#871982)

[Original report](https://bugs.launchpad.net/bugs/871982) created by **Langdon White (lwhite)**
```
I am running IIS 6.5 on Windows Server 2003 (don't ask why, long story)
with a self-signed certificate. I cannot get duplicity to connect to some
webdavs directories to do backups. I believe it is the IIS thing or the
self-signed thing. I am not sure which. I can say though that cadavar
connects fine (after yelling at me about the self-signed cert). Would love
ideas or a fix (if its a bug and not a problem between keyboard and back of
chair). "Using WebDAV protocol http" also seems a little weird.

uname -a: Linux thor 2.6.38-11-generic #50-Ubuntu SMP Mon Sep 12 21:17:25
UTC 2011 x86_64 x86_64 x86_64 GNU/Linux

Log from verbosity 9 (with some names changed: "user" and "backup-host")

Using archive dir:
/home/user/.cache/duplicity/36616c01a8fe379d2d6a7b6162a3c680
Using backup name: 36616c01a8fe379d2d6a7b6162a3c680
Import of duplicity.backends.ftpbackend Succeeded
Import of duplicity.backends.webdavbackend Succeeded
Import of duplicity.backends.hsibackend Succeeded
Import of duplicity.backends.tahoebackend Succeeded
Import of duplicity.backends.sshbackend Succeeded
Import of duplicity.backends.giobackend Succeeded
Import of duplicity.backends.ftpsbackend Succeeded
Import of duplicity.backends.localbackend Succeeded
Import of duplicity.backends.rsyncbackend Succeeded
Import of duplicity.backends.cloudfilesbackend Succeeded
Import of duplicity.backends.imapbackend Succeeded
Import of duplicity.backends.botobackend Succeeded
Using WebDAV host backup-host
Using WebDAV directory /dav/Backups/thor/
Using WebDAV protocol http
Main action: inc
================================================================================
duplicity 0.6.13 (April 02, 2011)
Args: /usr/bin/duplicity --verbosity 9 --no-encryption /home/user/Documents
webdavs://user@backup-host/dav/Backups/thor/
Linux thor 2.6.38-11-generic #50-Ubuntu SMP Mon Sep 12 21:17:25 UTC 2011
x86_64 x86_64
/usr/bin/python 2.7.1+ (r271:86832, Apr 11 2011, 18:13:53)
[GCC 4.5.2]
================================================================================
Using temporary directory /tmp/duplicity-5ewB0q-tempdir
Registering (mkstemp) temporary file /tmp/duplicity-5ewB0q-tempdir/mkstemp-
njwpv6-1
Temp has 17844174848 available, backup will use approx 34078720.
Listing directory /dav/Backups/thor/ on WebDAV server
WebDAV PROPFIND attempt #1 failed: 200
Listing directory /dav/Backups/thor/ on WebDAV server
WebDAV PROPFIND attempt #2 failed: 400 Bad Request
Listing directory /dav/Backups/thor/ on WebDAV server
Removing still remembered temporary file
/tmp/duplicity-5ewB0q-tempdir/mkstemp-njwpv6-1
Traceback (most recent call last):
  File "/usr/bin/duplicity", line 1265, in <module>
    with_tempdir(main)
  File "/usr/bin/duplicity", line 1258, in with_tempdir
    fn()
  File "/usr/bin/duplicity", line 1159, in main
    sync_archive()
  File "/usr/bin/duplicity", line 931, in sync_archive
    remlist = globals.backend.list()
  File "/usr/lib/python2.7/dist-
packages/duplicity/backends/webdavbackend.py", line 165, in list
    response = self.request("PROPFIND", self.directory, self.listbody)
  File "/usr/lib/python2.7/dist-
packages/duplicity/backends/webdavbackend.py", line 107, in request
    response = self.conn.getresponse()
  File "/usr/lib/python2.7/httplib.py", line 1015, in getresponse
    raise ResponseNotReady()
ResponseNotReady
```

Story points: 6.0