`clip.capture` errors out on Windows when new value == old value

[jcaw]

For example, in this block:

    with clip.capture() as s:
        actions.edit.copy()
    return s.get()

If the copied text is the same as the existing text in the clipboard, it will produce an error because it thinks there is no new text.

[lunixbochs]

should be fixed in current beta