title: Leaflet Markercluster - tooltip on hover issue
body: <p>I'm a newbie of javascript, trying to build an interactive map online, where some events should be triggered by clicking on markers and some just by hovering them. 
  Managed to have the click part working, but, because of Markercluster plugin, I'm not sure where to use onEachFeature function for having the tooltip opened by hover a single marker.
  Anyone please can tell me what I'm doing wrong?</p>
  
  <pre><code>var geoJsonFeature = {
    type: 'FeatureCollection',
    features: 
     [
      {
      type: 'Feature',
      properties: {
          title: 'Title',
          page: 'some.html',
          'marker-color': '#000000',
          zoom: 7
      },
      geometry: {
          type: 'Point',
          coordinates: [12.583745,55.6750803]
      }
  },
  ...
  };
  
  // access to mapbox api
  L.mapbox.accessToken ='...';
  var map = L.mapbox.map('map', 'example1234').setView([34, -37], 3);
  
  function getTitle(marker) {
      return marker.feature.properties.title;
  };
  
  function getPage(marker) {
      return marker.feature.properties.page;
  };
  
  var markerGroup = new L.MarkerClusterGroup({showCoverageOnHover:false});
  
  var geoJsonLayer = L.geoJson(geoJsonFeature, {
    onEachFeature: function (feature, layer) {
      var popupContent = getTitle(marker);
      layer.bindPopup(popupContent);
    }
  });
  
  markerGroup.addLayer(geoJsonLayer);
  
  map.addLayer(markerGroup);
  
  markerGroup.on('click', function(ev) {
    var marker = ev.layer;
  
    marker.on('click', function(ev) {
      if(map.getZoom() &gt; marker.feature.properties.zoom) {
          map.setView(ev.latlng, map.getZoom());   
      } 
      else {
          map.setView(ev.latlng, marker.feature.properties.zoom);
      }
     });
    });
  });
  
  geoJsonLayer.on('mouseover', function(e) {
    e.layer.openPopup();
  });
  
  geoJsonLayer.on('mouseout', function(e) {
    e.layer.closePopup();
  });
  </code></pre>