I switched over to the getopts crate on crates.io, instead of Rust's
private implementation. This will allow coreutils to build for Rust 1.0.
I'm splitting the updates into several commits for easier reviewing.
In addition to upgrading to the nightly build, I refactored the method
that creates the directories by switching from a recursive approach to
an iterative one. I also replaced the obsolete fs::mkdir() with a custom
method using fs::create_dir() and libc::chmod(). I added several
diagnostic messages that match the GNU implementation.