https://android-review.googlesource.com/102253

• permit interrupts during a write(2) loop in the cat builtin, too,
  not just in the read(2) loop – fixes inability to kill a clogged
  output cat

• kill the cat when smores finish

TODO: revisit this ⓐ in more depth, ⓑ for other functions, such as
      “hd”, and ⓒ test on AOSP as well