[1.4.x] Post release version bump.
[1.4.x] Added dates to release notes of today's release.

Backport of 68d264059abb21b96c4fe68bf4d99520268a451c from master
[1.4.x] Dropped fix_IE_for_vary/attach.

This is a security fix. Disclosure following shortly.
[1.4.x] Added additional checks in is_safe_url to account for flexible parsing.

This is a security fix. Disclosure following shortly.
Added release notes for 1.4.13.
Bumped version numbers for release.
Merge tag '1.4.13' into nonrel-1.4

Django 1.4.13