Unpoly now shows a progress bar that appears for late requests.
The progress bar is enabled by default. If you're using unpoly-migrate.js, the progress bar is disabled if you have an up:request:late listener, assuming that you have built a custom loading indicator.
For new layers, the [up-history-visible] and [up-history] options have been unified into a single [up-history] option. This reverts to the old behavior of Unpoly 1.0. The separation into two options was introduced in Unpoly 2.0, but turned out to be confusing to users.
