Windows problems with unpacking git repos

[Jake-Shadle]

[2019-07-26T17:27:46Z INFO  cargo_fetcher::cmds::sync] syncing crates.io index
[2019-07-26T17:27:46Z INFO  cargo_fetcher::sync] synchronizing 437 crates...
[2019-07-26T17:27:46Z INFO  cargo_fetcher::sync] skippipng crates.io-index download, index repository already present
[2019-07-26T17:27:46Z INFO  cargo_fetcher::cmds::sync] successfully synced crates.io index
[2019-07-26T17:27:46Z INFO  cargo_fetcher::sync] checking local cache for missing crates...
[2019-07-26T17:27:46Z INFO  cargo_fetcher::sync] synchronizing 434 missing crates...
[2019-07-26T17:27:49Z ERROR cargo_fetcher::sync] failed to unpack dependency cpal-0.9.0(git): failed to unpack: failed to unpack `C:\Users\ContainerAdministrator\.cargo\git/db\cpal-a7ffd7cabefac714\objects\pack\pack-c8fae354ebdeace6800253b30ea8fa1608b132bf.idx`
[2019-07-26T17:27:54Z ERROR cargo_fetcher::sync] failed to unpack dependency crossbeam-utils-0.6.5(git): failed to unpack: failed to unpack `C:\Users\ContainerAdministrator\.cargo\git/db\crossbeam-5d5b005504a37dac\objects\pack\pack-60c51cb402b51a9bfcaa68827fb9802a1b6a4869.pack`
[2019-07-26T17:27:56Z ERROR cargo_fetcher::sync] failed to unpack dependency lmdb-sys-0.8.0(git): failed to unpack: failed to unpack `C:\Users\ContainerAdministrator\.cargo\git/db\lmdb-rs-958662b5696e3642\objects\pack\pack-ef9004cd65ff43596b2e7fd12207adebb3518225.pack`
[2019-07-26T17:28:22Z INFO  cargo_fetcher::cmds::sync] finished syncing crates

> cargo fetch
    Updating git repository `https://github.com/EmbarkStudios/cpal`
    Updating git repository `https://github.com/crossbeam-rs/crossbeam`
    Updating git repository `https://github.com/EmbarkStudios/lmdb-rs.git`

[Jake-Shadle]

I think this is due to tar trying to preserve r/w permissions, which on windows means the read only flag is set on the directory, prior to writing children. You can use the set_preserve_permissions to ignore permissions on the files in the tar, but that was being ignored on Windows, so I made a PR alexcrichton/tar-rs#216 to fix that at least. It should be fine to completely ignore permissions on the source tarballs.