modify overwrite_specials attribute in schema

data/schema/game_config.cfg

@@ -36,6 +36,10 @@
         name="ability_apply"
         value="self|opponent|attacker|defender|both"
     [/type]
+    [type]
+        name="ability_overwrite"
+        value="none|one_side|both_sides"
+    [/type]
     [type]
         name="addon_type"
         value="sp|mp|hybrid"

data/schema/units/abilities.cfg

@@ -5,7 +5,7 @@
 		max=infinite
 		super="units/unit_type/abilities/~generic~,units/unit_type/attack/specials/" + {NAME}
 		{FILTER_TAG "filter_student" unit {FILTER_TAG "filter_weapon" weapon ()}}
-		{SIMPLE_KEY overwrite_specials bool}
+		{DEFAULT_KEY overwrite_specials ability_overwrite none}
 	[/tag]
 #enddef