kill test server with KILL rather than QUIT

Using QUIT will cause perl on win32 to spew warnings "Terminating on
signal SIGQUIT". We don't need the process to shut down gracefully, so
we can just kill it using KILL, which avoids these messages.

Author: haarg

t/lib/TestServer.pm

@@ -71,7 +71,7 @@ sub stop {
     my $pid = delete $self->{pid} or return;
     my $io = delete $self->{io};
 
-    kill 'QUIT', $pid;
+    kill 'KILL', $pid;
     close $io;
 
     waitpid $pid, 0;