use button elements instead of anchor elements and add tooltips to zoomcontrol

src/ol/control/zoomcontrol.js

@@ -38,26 +38,28 @@ ol.control.Zoom = function(opt_options) {
       options.zoomOutLabel : '\u2212';
 
   var tTipZoomIn = goog.dom.createDom(goog.dom.TagName.SPAN, {
-          'class':'', 
-          'role':'tooltip'
-      },"Zoom in");
+    'class': '',
+    'role' : 'tooltip'
+  }, 'Zoom in');
   var inElement = goog.dom.createDom(goog.dom.TagName.BUTTON, {
     'class': className + '-in olHasToolTip',
-    'name' : 'zoomIn'
+    'name' : 'ZoomIn',
+    'type' : 'button'
   }, tTipZoomIn, zoomInLabel);
-  
+
   goog.events.listen(inElement, [
     goog.events.EventType.TOUCHEND,
     goog.events.EventType.CLICK
   ], goog.partial(ol.control.Zoom.prototype.zoomByDelta_, delta), false, this);
 
   var tTipsZoomOut = goog.dom.createDom(goog.dom.TagName.SPAN, {
-          'class':'', 
-          'role':'tooltip'
-      }, "Zoom out");
+    'class': '',
+    'role' : 'tooltip',
+    'type' : 'button'
+  }, 'Zoom out');
   var outElement = goog.dom.createDom(goog.dom.TagName.BUTTON, {
     'class': className + '-out  olHasToolTip',
-    'name' : 'zoomOut'
+    'name' : 'ZoomOut'
   }, tTipsZoomOut, zoomOutLabel);
   goog.events.listen(outElement, [
     goog.events.EventType.TOUCHEND,