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.

include/qtext.h

@@ -106,6 +106,7 @@ struct	qtlists {
 #define QT_DEMONIC	30
 #define QTN_DEMONIC	20
 
+#define QT_BANISHED	60
 #endif	/***** !MAKEDEFS *****/
 
 #endif /* QTEXT_H */