Borg: llfuseのインストールに失敗する

インストール手順に従うと、llfuseのインストールに失敗します。

[979]anarcat<strong i="6">@marcos</strong>:src$ virtualenv --python=python3 borg-env
Already using interpreter /usr/bin/python3
Using base prefix '/usr'
New python executable in borg-env/bin/python3
Also creating executable in borg-env/bin/python
Installing setuptools, pip...done.
[980]anarcat<strong i="7">@marcos</strong>:src$ source borg-env/bin/activate
(borg-env)[982]anarcat<strong i="8">@marcos</strong>:src$ pip install sphinx
[...]
(borg-env)[983]anarcat<strong i="9">@marcos</strong>:src$ pip install 'llfuse<0.41'
Downloading/unpacking llfuse<0.41
  Downloading llfuse-0.40.tar.bz2 (454kB): 454kB downloaded
  Running setup.py (path:/tmp/pip-build-nbzu7cda/llfuse/setup.py) egg_info for package llfuse
    Package fuse was not found in the pkg-config search path.
    Perhaps you should add the directory containing `fuse.pc'
    to the PKG_CONFIG_PATH environment variable
    No package 'fuse' found
Cleaning up...
No files/directories in /tmp/pip-build-nbzu7cda/llfuse/pip-egg-info (from PKG-INFO)
Storing debug log for failure in /home/anarcat/.pip/pip.log

アーカイブに実際にfuse.pcが含まれていないことを確認できます（それが一体何であるかはわかりません）。

(borg-env)[987]anarcat<strong i="14">@marcos</strong>:src$ wget https://pypi.python.org/packages/source/l/llfuse/llfuse-0.40.tar.bz2#md5=bd8d07ddb6061ab03816e636efa37b5b
[...]
(borg-env)[988]anarcat<strong i="15">@marcos</strong>:src$ tar jft llfuse-0.40.tar.bz2  | grep fuse.pc
(borg-env)[989]anarcat<strong i="16">@marcos</strong>:src$ # nothing here.

なぜヒューズは特別なのですか？ なぜそれは通常の要件ファイルの一部ではないのですか？