`fdopendir` takes ownership of a directory file descriptor instead of
opening one with a path. `fdclosedir` is a FreeBSD extension that
transfers ownership of the file descriptor in DIR to the user.
This will allow us to redefine the exit function.
For example:
```
#define exit(code) { \
fprintf(stderr, "%s:%d: exit(%s) in function ‘%s’\n",
__FILE__, __LINE__, #code, __func__); \
_exit(code); \
}
```
Josh Megnauth