
curl_easy_duphandle() was not properly duping the ares channel. The ares_dup() function was introduced in c-ares 1.6.0 so by starting to use this function we also raise the bar and require c-ares >= 1.6.0 (released Dec 9, 2008) for such builds. Reported by: Ning Dong Bug: http://curl.haxx.se/mail/lib-2010-08/0318.html