Here's a patch that does the vertical split. It doesn't put any delimiter between the windows, which can be disconcerting, since when you first create the new region (^A V), absolutely nothing noticeable happens. But if you ^A-tab you'll be in the new region, and a next will make something show up. This was a diff against 4.0.3, which I gather from Michael's comment may be the wrong thing to diff
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