Improve peer host name resolution (closes #360)

- Take a QString in argument to avoid converting it twice. The caller already
  has the IP as a QString.
- Fix bug where hostnames coming from the cache would not the displayed.
- Fix bug where the resolved hostnames would not be displayed if the IP we know
  does not match the first one in the QHostInfo::addresses() list. It may come
  later in the list or may be formatted differently (possible with IPv6).
- Avoid requesting again host names for IPs that were already requested recently
  but whose resolution did not return a useful hostname.

src/properties/peerlistwidget.cpp

@@ -325,12 +325,15 @@ void PeerListWidget::loadPeers(const QTorrentHandle &h, bool force_hostname_reso
       updatePeer(peer_ip, peer);
       old_peers_set.remove(peer_ip);
       if (force_hostname_resolution && m_resolver) {
-        m_resolver->resolve(peer.ip);
+        m_resolver->resolve(peer_ip);
       }
     } else {
       // Add new peer
       m_peerItems[peer_ip] = addPeer(peer_ip, peer);
       m_peerEndpoints[peer_ip] = peer.ip;
+      // Resolve peer host name is asked
+      if (m_resolver)
+        m_resolver->resolve(peer_ip);
     }
   }
   // Delete peers that are gone
@@ -350,9 +353,6 @@ QStandardItem* PeerListWidget::addPeer(const QString& ip, const peer_info& peer)
   m_listModel->insertRow(row);
   m_listModel->setData(m_listModel->index(row, PeerListDelegate::IP), ip);
   m_listModel->setData(m_listModel->index(row, PeerListDelegate::IP_HIDDEN), ip);
-  // Resolve peer host name is asked
-  if (m_resolver)
-    m_resolver->resolve(peer.ip);
   if (m_displayFlags) {
     const QIcon ico = GeoIPManager::CountryISOCodeToIcon(peer.country);
     if (!ico.isNull()) {