Merge branch 'upnp-broken-refresh'.
This enhances the handling of buggy UPnP IGDs (i.e. routers) which do not allow refreshing still available mappings before their leases time out (see [here]). This showed up as the mapping being intermittently on and off for periods of approximately 3 minutes. : https://github.com/miniupnp/miniupnp/issues/131 Now such buggy IGDs are identified and if they are the only IGDs responding, then the client waits right until its (oldest) mapping times out, then adds an equivalent mapping. Clients now identify their mappings as `Ouinet-xxxx`, with `xxxx` being a random hex value which changes on each run (it is shown in debug messages). Other minor logging enhancements have been added too.