Destroy remaining items when a pane is destroyed

spec/pane-model-spec.coffee

@@ -107,9 +107,15 @@ describe "PaneModel", ->
     [pane1, container] = []
 
     beforeEach ->
-      pane1 = new PaneModel(items: ["A"])
+      pane1 = new PaneModel(items: [new Model, new Model])
       container = new PaneContainerModel(root: pane1)
 
+    it "destroys the pane's destroyable items", ->
+      [item1, item2] = pane1.items
+      pane1.destroy()
+      expect(item1.isDestroyed()).toBe true
+      expect(item2.isDestroyed()).toBe true
+
     describe "if the pane's parent has more than two children", ->
       it "removes the pane from its parent", ->
         pane2 = pane1.splitRight()

src/pane-model.coffee

@@ -142,6 +142,7 @@ class PaneModel extends Model
 
   # Private: Called by model superclass
   destroyed: ->
+    item.destroy?() for item in @items.slice()
     @parent.focusNextPane() if @focused
 
   # Public: Prompt the user to save the given item.