The upstream git.git project currently identifies all references inside
of `refs/bisect/` as well as `HEAD` as per-worktree references. This is
already incorrect and is currently being fixed by an in-flight topic
[1]. The new behavior will be to match all pseudo-references outside of
the `refs/` hierarchy as well as `refs/bisect/`.

Our current behavior is to mark a selection of pseudo-references as
per-worktree, only. This matches more pseudo-references than current
git, but forgets about `refs/bisect/`. Adjust behavior to match the
in-flight topic, that is classify the following references as
per-worktree:

- everything outside of `refs/`
- everything inside of `refs/bisect/`

[1]: <20170213152011.12050-1-pclouds@gmail.com>