fix the alarm()-based DNS timeout
Looking at the code of Curl_resolv_timeout() in hostip.c, I think that in case of a timeout, the signal handler for SIGALRM never gets removed. I think that in my case it gets executed at some point later on when execution has long left Curl_resolv_timeout() or even the cURL library. The code that is jumped to with siglongjmp() simply sets the error message to "name lookup timed out" and then returns with CURLRESOLV_ERROR. I guess that instead of simply returning without cleaning up, the code should have a goto that jumps to the spot right after the call to Curl_resolv().
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