Add back response headers to debug log

Also added an integration test to ensure we don't remove
this feature in the future.
Merge branch 'response-headers' into develop

* response-headers:
  Add back response headers to debug log
Bumping version to 0.68.0
Merge branch 'release-0.68.0' into develop

* release-0.68.0:
  Bumping version to 0.68.0
Add register_first/register_last in hooks module

Makes it possible to register hooks that you want called
before/after other hooks.
Refactor check_for_200_error to use register_first

No function change, this refactoring uses the new
register_first() method to ensure that we will always
be called before the general retry handlers.