Fix the knockback effect for TRoW's WML plague

(and add some horse cantering to boot)

changelog

@@ -17,6 +17,7 @@ CVS HEAD:
  * terrain improvements     
    * New forest tiles
  * fixed the description of traits in the help & tutorial
+ * fixed the 'knockback' for WML Plague in TRoW
  
 Version 0.9.0:
  * user interface improvements:

data/scenarios/The_Rise_of_Wesnoth/The_Midlands.cfg

@@ -348,6 +348,10 @@
 
 	[event]
 	name=victory
+		[sound]
+		name=horse-canter.wav
+		[/sound]
+
 		[move_unit_fake]
 			type=Knight
 			x=40,39,38,37,36,35,34,33,32,31,30

data/scenarios/The_Rise_of_Wesnoth/The_River_Road.cfg

@@ -417,6 +417,10 @@ Enter at Your Own Risk!"
 	[event]
 	name=victory
 
+		[sound]
+		name=horse-canter.wav
+		[/sound]
+
 		[move_unit_fake]
 			type=Knight
 			x=35,34,33,32,31,30

data/scenarios/The_Rise_of_Wesnoth/trow-macros.cfg

@@ -80,6 +80,15 @@
 			[/not]
 		[/filter_second]
 
+		[store_unit]
+		variable=dead_store
+		kill=yes
+		[filter]
+			x={X}
+			y={Y}
+		[/filter]
+		[/store_unit]
+
 #ifdef EASY
 		[unit]
 			description=A Former Friend
@@ -124,5 +133,7 @@
 				{TRAIT_LOYAL}
 			[/modifications]
 		[/unit]
+
+		{CLEAR_VARIABLE dead_store}
 #endif
 #enddef