libtar: add --numeric-owner option

We are not going to use this anymore in CWM like it was with mini config from Busybox
This way, the restore can be done based on user/group name rather than to uid/gid
This could potentially cause some applications to be broken when restored to a different ROM/system
dedupe: merge clean up code from @xiaolu
fix restorecon_from_file potential crash (by @xiaolu)
(only for BOARD_RECOVERY_USE_BBTAR)
fix 240x320 images