Switch to using the `change-preview()` action that was introduced in
0.29.0 (which was actually not yet released for a year when this feature
was first written). The old `preview()` is a one-off action while
`change-preview()` changes the `--preview` option.
This had the downside that when changing to a different preview and
moving to the next commit one would had to repeat the change. This was
especially annoying when looking through the history of a file that was
renamed. With the commit that renamed the file all previous commits
broke in the `files_only` preview as the path didn't exist yet (A
possible but probably pretty hard TODO to fix).
TODO: glog: Fix files_only preview for renamed files or give prompt to
change the paths