le 1 or 2 (parameter `which`), stripping off line
    prefixes.

    Examples:

    >>> diff = ndiff('one\ntwo\nthree\n'.splitlines(keepends=True),
    ...              'ore\ntree\nemu\n'.splitlines(keepends=True))
    >>> diff = list(diff)
    >>> print(''.join(restore(diff, 1)), end="")
    one
    two
    three
    >>> print(''.join(restore(diff, 2)), end="")
    ore
    tree
    emu
    r