X-UA-Compatible is no longer breaking validation

Remove statement about X-UA-Compatible is breaking validation.
Insted of removing this, maybe we should just change it to something that informs users about the fact that some validators (e.g.:  [http://validator.nu/](http://validator.nu/?doc=http%3A%2F%2Fdemo.html5boilerplate.com)) might still complain about the `X-UA-Compatible` value.

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Thoughts ?