Tested against osx 10.9

I looked to see what version of libc OSX uses and apparently Apple is a bit cagey about it. There's this in the library header, but I don't think it means much to the outside world:

```
  cmd LC_SOURCE_VERSION
  cmdsize 16
  version 1197.1.1
```

`sys/termios.h` says

> Copyright (c) 2000-2006 Apple Computer, Inc. All rights reserved.

So it's probably compatible at-least with any OSX version that Rust can run on.