title: Window Scroll with drag and drop fail
body: <p>I try to make a infinite scroll but my scroll binding doesn't work perfectly... at all :(</p>
  
  <pre><code> var dragStart = function (event) {
  
          var downPosX = event.pageX;
          var downPosY = event.pageY;
          var oldposScroll = $(window).scrollTop();
  
          document.body.focus();
  
          var dragMove = function (event) {
              var movePosX = event.pageX;
              var movePosY = event.pageY;
              var deltaPosX = movePosX - downPosX;
              var deltaPosY = movePosY - downPosY;
              var movetop = oldposScroll + (deltaPosY * -1);
  
              console.log('[movePosY = ' +movePosY+']  [deltaPosY = ' +deltaPosY+']  [movetop = ' + movetop + '] ');
  
              $(window).scrollTop(movetop);
  
              downPosX = movePosX;
              downPosY = movePosY;
              oldposScroll = movetop;
          };
  
          var dragStop = function (event) {
              $(window).unbind('mousemove', dragMove).unbind('mouseup', dragStop);
          };
  
          $(window).mousemove(dragMove).mouseup(dragStop);
  
          event.preventDefault();
      };
  
  
  $(window).on("scroll", function (event) {
              console.log('rendering');
          });
  
  $viewport.mousedown(dragStart);
  </code></pre>
  
  <p>So I want to drag and drop my viewport (div) in order to scroll the document. That's works but I have  some crazy result when I print the delta value :</p>
  
  <pre><code>[movePosY = 552] [deltaPosY = 8] [movetop = 440]
  infini...port.js (ligne 33)
  [movePosY = 543] [deltaPosY = -9] [movetop = 449]
  infini...port.js (ligne 33)
  [movePosY = 551] [deltaPosY = 8] [movetop = 441]
  infini...port.js (ligne 33)
  [movePosY = 540] [deltaPosY = -11] [movetop = 452]
  infini...port.js (ligne 33)
  [movePosY = 550] [deltaPosY = 10] [movetop = 442]
  infini...port.js (ligne 33)
  [movePosY = 539] [deltaPosY = -11] [movetop = 453]
  infini...port.js (ligne 33)
  [movePosY = 549] [deltaPosY = 10] [movetop = 443] 
  </code></pre>
  
  <p>As you can see, instead of continuous negatives values, I have positives and negatives  values with big gap. </p>
  
  <p>I don't understand why... I suspect the window object to be too slow to bind "scroll" Event while mouseMove Event is already fire... but I don't know how resolve this bug...</p>
  
  <p>(Before that I have a overflow on my viewport with a scrollBar and I didn't have this bug. That's why I suspect the window Object)</p>