Make file(DOWNLOAD) fail on http error

If a http server responds with a result code greater than 400 then the
data returned from the download probably do not match that expected.
Teach file(DOWNLOAD) to fail with an error in this case instead of
silently pretending that the download worked.  The file(UPLOAD) command
already does this.

Source/cmFileCommand.cxx

@@ -2753,6 +2753,10 @@ cmFileCommand::HandleDownloadCommand(std::vector<std::string> const& args)
   ::CURLcode res = ::curl_easy_setopt(curl, CURLOPT_URL, url.c_str());
   check_curl_result(res, "DOWNLOAD cannot set url: ");
 
+  // enable HTTP ERROR parsing
+  res = ::curl_easy_setopt(curl, CURLOPT_FAILONERROR, 1);
+  check_curl_result(res, "DOWNLOAD cannot set http failure option: ");
+
   res = ::curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION,
                            cmWriteToFileCallback);
   check_curl_result(res, "DOWNLOAD cannot set write function: ");