Save As - document keep failure

- add a comment to explain the causes of keep failure,

- rename the keep failure response callback to fit convention,

- fix typo and whitespace nearby.

src/sugar3/activity/activity.py

@@ -851,7 +851,7 @@ class Activity(Window, Gtk.Container):
 
         This method is called by the close() method below. In general,
         activities should not override this method. This method is part of the
-        public API of an Acivity, and should behave in standard ways. Use your
+        public API of an Activity, and should behave in standard ways. Use your
         own implementation of write_file() to save your Activity specific data.
         '''
 
@@ -1048,6 +1048,11 @@ class Activity(Window, Gtk.Container):
         pservice.share_activity(self, private=private)
 
     def _show_keep_failed_dialog(self):
+        '''
+        A keep error means the activity write_file method raised an
+        exception before writing the file, or the datastore cannot be
+        written to.
+        '''
         alert = Alert()
         alert.props.title = _('Keep error')
         alert.props.msg = _('Keep error: all changes will be lost')
@@ -1060,11 +1065,11 @@ class Activity(Window, Gtk.Container):
         alert.add_button(Gtk.ResponseType.OK, _('Stop anyway'), stop_icon)
 
         self.add_alert(alert)
-        alert.connect('response', self._keep_failed_dialog_response_cb)
+        alert.connect('response', self.__keep_failed_dialog_response_cb)
 
         self.reveal()
 
-    def _keep_failed_dialog_response_cb(self, alert, response_id):
+    def __keep_failed_dialog_response_cb(self, alert, response_id):
         self.remove_alert(alert)
         if response_id == Gtk.ResponseType.OK:
             self.close(skip_save=True)