Add a small timeout to fslock aquisition

If we don't get our fslock immediately on starting a TorClient, we currently exit. In many circumstances, applications would likely prefer us to try again for a short time, to avoid race conditions if they don't call TorClient::wait_for_close (see #1418 (closed)).

IMO this needs to be configurable, since in many circumstances, applications would like to know immediately if they don't have the lock.