Make sure there's no pidfile if we cannot start the initial sockfilt tool -

this happens for some ipv6-enabled hosts on which sockfilt cannot listen
on ipv6.

tests/ftpserver.pl

@@ -128,11 +128,12 @@ sub startsf {
     open(STDOUT, ">&SFWRITE")   || die "can't dup client to stdout";
 }
 
-startsf();
+# remove the file here so that if startsf() fails, it is very noticable 
+unlink(".ftp$ftpdnum.pid");
 
-logmsg sprintf("FTP server started on port IPv%d/$port\n",
-               $ipv6?6:4);
+startsf();
 
+logmsg sprintf("FTP server started on port IPv%d/$port\n", $ipv6?6:4);
 open(PID, ">.ftp$ftpdnum.pid");
 print PID $$;
 close(PID);