'Initialize the command and stash away values for use in do()'

def __init__(self):

    ModelCommand.__init__(self)
    self.old_diff_text = self.model.diff_text
    self.old_filename = self.model.filename
    self.old_mode = self.model.mode
    self.new_diff_text = self.old_diff_text
    self.new_filename = self.old_filename
    self.new_mode = self.old_mode
