Tar could not handle the headers.

This reverts parts of commit 8b1a5301.
Keep the usage fixes.

and relocate the place of the symlink in tar header, as symlink
use the linkname field. now it's split to devmajor, devminor and
padding fields.

- ability to embed an checksum inside the tar header for regular
  files (to avoid checksumming at apk installation time)
- way to remove the end-of-archive marker to create concenatable
  .tar.gz:s for signed apks