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.

dat/quest.txt

@@ -3459,7 +3459,21 @@ essential in locating the Amulet of Yendor."
 %Cp - 00049
 "Why search for the Amulet?  Thou wouldst but lose it, cretin."
 %E
+#
+#	Banishment message (for converted hero)
+#
+%Cc - 00060
+"You have betrayed all those who hold allegiance to %d, as you once did.
+My allegiance to %d holds fast and I cannot condone or accept what you 
+have done.
 
+Leave this place.  You shall never set foot at %H again.
+That which you seek is now lost forever, for without the Bell of Opening, 
+you will never be able to enter the place where he who has the Amulet 
+resides.
+
+Go now!  You are banished from this place.
+%E
 #
 #	TEST PATTERN
 #