Unit Tests

- Modified the test_hooks/* scripts to use /bin/sh, which is portable. When
  using /bin/bash, Cygwin and FreeBSD silently fail.

test/test_hooks/on-exit-bad

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/bin/sh
 
 # The on-exit event is triggered once, after all processing is complete.
 # This hooks script has no effect on processing.