Check for valid IP for known proxies.

[bitbound]

Closes #813

Until the next release, make sure all IP addresses in KnownProxies are valid.

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This makes it easier for other entities to use the software because they only have to deal with one copyright holder. It also gives me assurance that we'll be able to make decisions in the future without gathering and consulting all contributors.

While this may seem odd, many open source maintainers practice this. Here are a couple well-known examples:

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A nice article on the topic can be found here: https://haacked.com/archive/2006/01/26/WhoOwnstheCopyrightforAnOpenSourceProject.aspx/

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