Add a step to revert unsaved changes

I took the key part from PR #3183 and added it to the post-confirmation
flow.

src/editor.coffee

@@ -450,7 +450,9 @@ class Editor extends Model
       else
         confirmed = true
 
-      repo.checkoutHead(filePath) if confirmed
+      if confirmed
+        @buffer.reload() if @buffer.isModified()
+        repo.checkoutHead(filePath)
 
   # Copies the current file path to the native clipboard.
   copyPathToClipboard: ->