fix #H7226 - vault guard should have whistle

fix #H7226 - vault guard should have whistle

Implement the suggestion that since teleporting away from the vault
while being confronted by the guard results in a shrill whistling
sound, the vault guard ought to have a tin whistle in his inventory.

I also added a check that he does have the whistle and to give an
alternate message if not, but after half a dozen tries to have a
squad of beefed up monkeys steal the whistle, they never accomplished
that.  At least three times they took everything except the whistle
but I never succeeded in verifying the alternate message.