From 1.x to 2.x
---------------
Upgrading from CDN integration 1.x to 2.x requires applying a new core patch.
Alternatively, there is now a new type of CDN integration that does not
require a core patch, instead it relies on the theme layer to alter file URLs.
It is slower and won't be able to alter *all* file URLs, but it is easier to
use. When the module detects that the patch is not applied, it will
automatically fall back to this mechanism.
Also note that the core patch is already included in Pressflow!

The recommended steps to update your Drupal site are:
1) Copy the 1.x core patch (patches/drupal6.patch) to the Drupal root directory.
2) Revert the 1.x core patch:
    patch -p0 -R < drupal6.patch
3) Disable CDN integration at admin/settings/cdn.
4) Update the CDN integration module code.
5) Copy the 2.x core patch (patches/drupal6.patch) to the Drupal root directory.
6) Apply the 2.x core patch:
    patch -p0 < drupal6.patch
7) Re-enable CDN integration at admin/settings/cdn.

The ImageCache module patch has remained unchanged since version 1.x. When you
did not apply the core patch and thus want to rely on the theme layer fallback
mechanism, you don't have to apply the ImageCache module patch either.
But when you update to an ImageCache version that's newer than 2.0 beta 10,
you will have to apply the alternative patch: patches/imagecache_6--2.patch.