fix for 'map elements are selected in IE when using shift key' in drag

handler from pierre.
Confirmed that this can be tested simply by using anything with a drag handler
in IE, so it will get caught in acceptance test. 
(Closes #792)


git-svn-id: http://svn.openlayers.org/trunk/openlayers@4230 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Handler/Drag.js

@@ -153,6 +153,12 @@ OpenLayers.Handler.Drag = OpenLayers.Class(OpenLayers.Handler, {
             this.down(evt);
             this.callback("down", [evt.xy]);
             OpenLayers.Event.stop(evt);
+            
+            if(!this.oldOnselectstart) {
+                this.oldOnselectstart = document.onselectstart;
+                document.onselectstart = function() {return false;}
+            }
+            
             return false;
         }
         return true;