Now uses sigsetjmp() and siglongjmp() to bail out from slow name lookups in

case a timeout is set. This seems to work. God knows if it is good enough
or what kind of side-effects we introduce here and now.

I'll close my eyes and cross my fingers. Hard.

lib/hostip.c

@@ -56,6 +56,10 @@
 #endif
 #endif
 
+#ifdef HAVE_SETJMP_H
+#include <setjmp.h>
+#endif
+
 #include "urldata.h"
 #include "sendf.h"
 #include "hostip.h"
@@ -191,6 +195,11 @@ hostcache_prune(curl_hash *hostcache, int cache_timeout, int now)
   return (__v); \
 }
 
+#ifdef HAVE_SIGSETJMP
+/* Beware this is a global and unique instance */
+sigjmp_buf curl_jmpenv;
+#endif
+
 Curl_addrinfo *Curl_resolv(struct SessionHandle *data,
                            char *hostname,
                            int port)
@@ -201,6 +210,14 @@ Curl_addrinfo *Curl_resolv(struct SessionHandle *data,
   time_t now;
   char *bufp;
 
+#ifdef HAVE_SIGSETJMP
+  if(sigsetjmp(curl_jmpenv, 1) != 0) {
+    /* this is coming from a siglongjmp() */
+    failf(data, "name lookup time-outed");
+    return NULL;
+  }
+#endif
+
   /* If the host cache timeout is 0, we don't do DNS cach'ing
      so fall through */
   if (data->set.dns_cache_timeout == 0) {