Extend Django detection using the csrfmiddlewaretoken in HTML forms

Sadly Django sites are hard to detect, as they have a policy of not leaking information. 
However, at pages with HTML `<form method="post">` tags, Django developers typically include the `csrfmiddlewaretoken` field in the form. This patch also includes detection for that feature.

Two remarks:
* This indication may not necessarily be present at all pages of the site.
* The order of layout of attributes is mirrored to how Firefox outputs the `innerHTML` code. The real source code uses single quotes and a different ordering of attributes.

Nevertheless I hope you find this enhancement useful and accept the patch.