Don't let button controls interfer with handlers.

This change involves removal of the map's eventsDiv and introduces an OpenLayers.Events.buttonclick component that adds a buttonclick event which makes sure that only events that are not related to clicking a button propagate. This allows button controls to be on the map's viewPortDiv again.

lib/OpenLayers/Util.js

@@ -416,6 +416,7 @@ OpenLayers.Util.createAlphaImageDiv = function(id, px, sz, imgURL,
     var div = OpenLayers.Util.createDiv();
     var img = OpenLayers.Util.createImage(null, null, null, null, null, null, 
                                           null, delayDisplay);
+    img.className = "olAlphaImg";
     div.appendChild(img);
 
     OpenLayers.Util.modifyAlphaImageDiv(div, id, px, sz, imgURL, position,