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.

tests/list-tests.html

@@ -46,6 +46,7 @@
     <li>Control/PanPanel.html</li>
     <li>Control/SLDSelect.html</li>
     <li>Events.html</li>
+    <li>Events/buttonclick.html</li>
     <li>Extras.html</li>
     <li>Feature.html</li>
     <li>Feature/Vector.html</li>