render::unpack fails for some images.

[akhramov]

Hi, thanks for your awesome library! I think I found a little bug, described below. Aside from that -- great overall experience, thanks!

Description Alpine-based images make a heavy use of symlinks. As it stands now, tar-rs overwrites files and not symlinks. (alexcrichton/tar-rs/pull/217) If layers create a symlink in the same location, render::unpack will fail.

Steps to reproduce:

1. Run cargo run --example image registry-1.docker.io nginxdemos/hello

Expected result:

1. Layers are downloaded and unpacked

Actual result:

1. The command fails with

[registry-1.docker.io] failed to unpack `/usr/home/akhramov/dkregistry-rs/nginxdemos_hello:latest/usr/bin/strings`

Known workaround:

None yet, shall tar-rs be fixed?