Improve handling of pending items when moving items b/t panes

* Make pending items permanent when moved to new panes
* Ensure existing pending items are not destroyed when a new
  item is added to the same pane

Signed-off-by: Michelle Tilley <binarymuse@github.com>

spec/pane-spec.coffee

@@ -680,6 +680,23 @@ describe "Pane", ->
           expect(pane2.isDestroyed()).toBe true
           expect(item4.isDestroyed()).toBe false
 
+    describe "when the item being moved is pending", ->
+      it "is made permanent in the new pane", ->
+        item6 = new Item("F")
+        pane1.addItem(item6, pending: true)
+        expect(pane1.getPendingItem()).toEqual item6
+        pane1.moveItemToPane(item6, pane2, 0)
+        expect(pane2.getPendingItem()).not.toEqual item6
+
+    describe "when the target pane has a pending item", ->
+      it "does not destroy the pending item", ->
+        item6 = new Item("F")
+        pane1.addItem(item6, pending: true)
+        expect(pane1.getPendingItem()).toEqual item6
+        pane2.moveItemToPane(item5, pane1, 0)
+        expect(pane1.getPendingItem()).toEqual item6
+
+
   describe "split methods", ->
     [pane1, item1, container] = []
 

src/pane.coffee

@@ -404,7 +404,7 @@ class Pane extends Model
     @setPendingItem(item) if pending
 
     @emitter.emit 'did-add-item', {item, index, moved}
-    @destroyItem(lastPendingItem) if lastPendingItem?
+    @destroyItem(lastPendingItem) if lastPendingItem? and not moved
     @setActiveItem(item) unless @getActiveItem()?
     item