specify posix.signal:

- before:

    sig = require "posix.signal"

- describe kill:

  - context with bad arguments:

      badargs.diagnose (sig.kill, "(int, ?int)")

- describe killpg:

  - context with bad arguments:

      badargs.diagnose (sig.killpg, "(int, ?int)")

- describe raise:

  - context with bad arguments:

      badargs.diagnose (sig.raise, "(int)")

- describe signal:

  - context with bad arguments:

      badargs.diagnose (sig.signal, "(int, ?function|string, ?int)")