The TarLib class has an license tag that states it is under “GPL”, without a version number. I wrote to the author, that explained that he wanted to release it under LGPL v2.1.
You can apply the attached patch or, at your wish, pull the branch contrib/license-tarlib from <git://git.ortolo.eu/pkg-dokuwiki.git>:
$ git pull git://git.ortolo.eu/pkg-dokuwiki.git
Maintainer of the Debian package