Added a new required ALLOWED_HOSTS setting for HTTP host header validation.

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

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

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

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

This is a security fix. Disclosure and advisory coming shortly.
Update 1.5 release notes for XML and formset fixes.