Various small changes

Some Christmas presents from yours truly:

- When fighting an armored opponent, attackers try to concentrate hits where
  they can hurt most (see news 2228)
  The chances of succeeding at this task now depend on how large the melee is:
  in a large melee, hits will now be targeted less accurately. One-on-one
  fights remain unchanged.

- You will see "r" in your prompt if someone is riding you

- Some ancient game messages have been changed, some missing messages
  on "rarely used" spells have been added