The constructor declares a new Archive_Tar
object, identifying it by the name of the tar file.
Parameter
string $tarname -
the name of the tar archive to work with
mixed $compress -
if TRUE, indicates that the archive is compressed (using gzip).
if NULL the archive is not compressed, if 'gz' or 'bz2', indicates
that the archive is compressed with gzip or bz2. For compatibility
reason the boolean value TRUE means 'gz'.
