[1.3.x] Added ALLOWED_HOSTS setting for HTTP host header validation.

This is a security fix; disclosure and advisory coming shortly.
[1.3.x] Restrict the XML deserializer to prevent network and entity-expansion DoS attacks.

This is a security fix. Disclosure and advisory coming shortly.
[1.3.x] Checked object permissions on admin history view.

This is a security fix. Disclosure and advisory coming shortly.

Patch by Russell Keith-Magee.
[1.3.x] Added a default limit to the maximum number of forms in a formset.

This is a security fix. Disclosure and advisory coming shortly.
Merge pull request #5 from matchbox/security-patches

Security patches