Uncompress safe archive

Check that, for one archive, no files are uncompressed outside of the
destination folder. If ok, the archive is considered safe.

If there are at least one, a ValueError is raised, thus stopping the
archive loading.

This follows reading the warning footnote in the tarfile.extractall api
https://docs.python.org/3.4/library/tarfile.html#tarfile.TarFile.extractall.

Note that the warning also exists for zipfile.extractall
(https://docs.python.org/3.4/library/zipfile.html#zipfile.ZipFile.extractall)
but is invalidated by the zipfile.extract api doc
(https://docs.python.org/3.4/library/zipfile.html#zipfile.ZipFile.extract)
and its implementation (extractall uses extract).