do-autosave in editor:backup-autosave<%>

This method is called to perform the autosaving. See also autosave:register

• (send an-editor:backup-autosave do-autosave) -> (union #f string)

  When the file has been modified since it was last saved and autosaving it turned on (via the autosave? method) an autosave file is created for this editor<%>.

  Returns the filename where the autosave took place, or #f if none did.