fallback for ip optional

[blodone]

With this commit it would be optional to provide a fallback for reliable IP information.
otherwise we would get an integrity error so with the attribute error the user knows whats going wrong

[coveralls]

Coverage decreased (-1.35%) to 92.57% when pulling b1932c2 on induux:master into 555144f on Bouke:master.

[coveralls]

Coverage decreased (-1.35%) to 92.57% when pulling b1932c2 on induux:master into 555144f on Bouke:master.

[Bouke]

Hi @blodone thanks again for your effort. Could you explain why you'd want to see the working of this changed? As I've explained elsewhere:

I don't think that merging your PR is a good idea, as Django doesn't include a similar middleware for good reasons. However I can see your need for a solution, so you could create a custom middleware that sets REMOTE_ADDR based on X-Forwarded-For. If the middleware appears before the user session middleware, everything works as intended.

[blodone]

i think for more then 50% of the people using this a module they need a way to get it working behind a proxy without writing own middleware to emulate REMOTE_ADDR just to supply django-user-sessions.

As i explained its optional, so it does not affect security unless you enable it explicitly in the settings.
Also the own middleware would also affect security, even though when bad written it exposes a greater security risk than enabling a fallback when REMOTE_ADDR is None

[coveralls]

Coverage decreased (-1.35%) to 92.57% when pulling 1da7b5e on induux:master into 555144f on Bouke:master.

[Bouke]

I won't merge this PR as explained above and in the issues I linked to. The goal of this package is to provide Session objects as first-class ORM models. How the IP address is derived from the request information is out-of-scope.