doomed quest

doomed quest
Your quest leader would tell you to return later, even after you
were converted, which would be futile, and could mislead new
players.

This patch:
1. Causes the quest leader to banish you the first time you
encounter him/her following a conversion, since you cannot ever
complete the quest anyway in the current game.
2. Adds a new general QT_BANISHED message to be delivered, in
which you are told that you won't be able to get the Amulet without
the Bell now.

This helps resolve the complaint about not knowing that your game
cannot be won.