tar: support -J, --xz explicit compression option

function                                             old     new   delta
tar_main                                             868     881     +13
tar_longopts                                         285     290      +5
packed_usage                                       29267   29270      +3

Signed-off-by: Boris Reisig <boris@boris.ca>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
1 file changed