We need to set `[trac] show_full_names = disabled` for the username
decoration plugin to continue working. We also want this settings for
other reasons, since we accept usernames in various fields, but the
usernames are not shown anymore with this feature enable.
Additionally, we need a newer version of the autocomplete users plugin.
See https://trac-hacks.org/ticket/13115. Unfortunately the plugin does not
yet have a release with this patch in, so we may have to install from