[9fans] get the last write offset in p9p acme

[Mathieu Lonjaret <mathieu.lonjaret@gmail.com>]

Hi,

After I've written a bunch of lines in an acme win ( with (w *Win)
Write("body",...), I need to know (and save) the position of the last
char I've written.
I need that position because I want everything I write afterwards to
be written there, and not appended. (constantly overwriting the last
thing that was written).

So the silly trick I've used to get that position is to first select
the whole text and then get the address of the end of the selection,
as the following:

	err = w.Addr("%s", "#0,")
	if err != nil {
		return err
	}
	_, pos, err := w.ReadAddr()

Is there a more direct way?

Thanks,
Mathieu