Add NSE for CVE-2017-9248

[hantwister]

This is a copy of the NSE I sent to nmap-dev on Friday night.

It attempts to detect web applications using a vulnerable version of the Telerik UI for ASP.NET AJAX library, which may lead to leaking the machine key (and subsequent view state compromise) and/or arbitrary file uploads (and subsequent RCE).

Comments/feedback/... welcome.

[dmiller-nmap]

This is a nice script. It is simple enough, though, that it could be converted into a fingerprint in nselib/data/http-fingerprints.lua. In this format, we would only do the '?dp=////' request for each possible endpoint, since the fingerprints format doesn't currently allow sending followup requests. Would this be a problem? It seems as though just checking for the "Base-64" string might be a solid-enough check. Please let us know if you intend to convert it, if you have any concerns about it, or if you want us to convert it and credit you.

[hantwister]

It's probably reasonable to assume that 404 pages and the like aren't going to generally discuss Base-64, and that hyphen would stop matches against data URIs that might be used, so I don't think it'll be a problem to just use the second check.

I've added a second commit that removes the NSE and adds the few appropriate lines to http-fingerprints.lua.