vim: re-enable long line highlighting
vim: re-enable long line highlighting

I inadvertantly turned this off in f06588f515af6d0ac092af00cfc72791d3
and just noticed:

https://twitter.com/wincent/status/946550661654523904

Also noticed that recent change in Neovim makes this a bit uglier, so
debating whether to forget about it for now:

https://github.com/neovim/neovim/issues/7383#issuecomment-354387145

Will think about it anyway...

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