When transferring 500 downloads in parallel with a c-ares enabled build only

to find that it crashed miserably, and this was due to some select()isms left
in the code. This was due to API restrictions in c-ares 1.3.x, but with the
upcoming c-ares 1.4.0 this is no longer the case so now libcurl runs much
better with c-ares and the multi interface with > 1024 file descriptors in
use.

lib/easy.c

@@ -420,11 +420,14 @@ CURLcode curl_easy_perform(CURL *easy)
     timeout.tv_sec = 1;
     timeout.tv_usec = 0;
 
-    /* get file descriptors from the transfers */
+    /* Old deprecated style: get file descriptors from the transfers */
     curl_multi_fdset(multi, &fdread, &fdwrite, &fdexcep, &maxfd);
-
     rc = Curl_select(maxfd+1, &fdread, &fdwrite, &fdexcep, &timeout);
 
+    /* The way is to extract the sockets and wait for them without using
+       select. This whole alternative version should probably rather use the
+       curl_multi_socket() approach. */
+
     if(rc == -1)
       /* select error */
       break;