missing directories in rustc-nightly-src tarball

[japaric]

STR

Download and unpack: http://static.rust-lang.org/dist/2016-02-17/rustc-nightly-src.tar.gz

It should contain the same files as 57c357d but it's missing the following directories: src/bootstrap, src/build_helper, src/rustc, src/grammar, etc. The files that are present in both cases are equal, so the tarball is only missing files. Perhaps a "whitelist" needs to be updated.

cc @alexcrichton