Please provide VertSplitNC for splits not adjacent to the current window

[joshtriplett]

I currently use different highlights for StatusLine and StatusLineNC, to brighten the status line of the current window, making it easy to see at a glance.

I'd love to do the same for the vertical splits surrounding the current window and non-current windows, making the former brighter than the latter.

The highlight VertSplit defines the highlight for the vertical split. I'd love to have a separate highlight VertSplitNC, used for any vertical split not adjacent to the current window.