message: FAPL: add core_filebacked() shortcut
diff: @@ -1173,6 +1173,12 @@ impl FileAccessBuilder {
  self.driver(&FileDriver::Core(drv))
  }
  + pub fn core_filebacked(&mut self, filebacked: bool) -> &mut Self {
  + let mut drv = CoreDriver::default();
  + drv.filebacked = filebacked;
  + self.driver(&FileDriver::Core(drv))
  + }
  +
  pub fn core(&mut self) -> &mut Self {
  self.driver(&FileDriver::Core(CoreDriver::default()))
  }
  