The value of ${seed_dir} may have spaces in it, making the current
argument string building method unsafe. Instead, use positional
parameters to pass these arguments safely.
There have been a number of subtle improvements and cleanups to seedrng,
including using openat and locking the directory fd instead of a
separate lock file. Also various stylistic cleanups.
This fixes#519.
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
