DM S07: Specify alternative objective and adjust difficulty

Also fixes dialog refering to 'stones' by ensuring all difficulies have at
least two stones. The addtional stone on easy is added where it can be
easily destroyed right away. A third stone is added on hard.

data/campaigns/Delfadors_Memoirs/scenarios/07_Night_in_the_Swamp.cfg

@@ -54,6 +54,7 @@
 
 #ifdef EASY
     {MEMOIRS_GENERATOR_SKELETON 18 3}
+    {MEMOIRS_GENERATOR_SKELETON 10 16}
 #endif
 
 #ifdef NORMAL
@@ -63,6 +64,7 @@
 
 #ifdef HARD
     {MEMOIRS_GENERATOR_SKELETON 18 3}
+    {MEMOIRS_GENERATOR_SKELETON 7 5}
     {MEMOIRS_GENERATOR_SKELETON 11 19}
 #endif HARD
 
@@ -99,6 +101,11 @@
                 condition=win
                 show_turn_counter=yes
             [/objective]
+            [objective]
+                {ALTERNATIVE_OBJECTIVE_CAPTION}
+                description=_ "Destroy the stones"
+                condition=win
+            [/objective]
             [objective]
                 description=_ "Death of Delfador"
                 condition=lose
@@ -112,6 +119,10 @@
                 bonus=yes
                 carryover_percentage=80
             [/gold_carryover]
+
+            [note]
+                description=_ "Mages and Paladins are capable of destroying the stones"
+            [/note]
         [/objectives]
     [/event]