python-django: multiple vulnerabilities

From the Django advisory:

Several earlier Django security releases focused on the issue of poisoning the HTTP Host header, causing Django to generate URLs pointing to arbitrary, potentially-malicious domains. In response to further input received and reports of continuing issues following the previous release, we're taking additional steps to tighten Host header validation.

Also following up on a previous issue: in July of this year, we made changes to Django's HTTP redirect classes, performing additional validation of the scheme of the URL to redirect to (since, both within Django's own supplied applications and many third-party applications, accepting a user-supplied redirect target is a common pattern). Since then, two independent audits of the code turned up further potential problems. So, similar to the Host-header issue, we are taking steps to provide tighter validation in response to reported problems (primarily with third-party applications, but to a certain extent also within Django itself).