An URL containing hex-encoded forward slash (%2F) causes
Wikipedia to go to a neverending sequence of 301 Moved Temporarily,
each adding a /wiki/ prefix.
HTTP/1.0 301 Moved Permanently
(...)
Location: http://cs.wikipedia.org/wiki/wiki/Foo%2FBar
(...)
etc.
Version: unspecified
Severity: minor
URL: http://cs.wikipedia.org/wiki/Foo%2FBar