make the drag handler and drag feature control tidy up after themselves - as a bonus, give the drag feature control an onStart method. Thanks for the review crschmidt (closes #950).

git-svn-id: http://svn.openlayers.org/trunk/openlayers@4147 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Handler/Drag.js

@@ -282,7 +282,10 @@ OpenLayers.Handler.Drag = OpenLayers.Class(OpenLayers.Handler, {
     deactivate: function() {
         var deactivated = false;
         if(OpenLayers.Handler.prototype.deactivate.apply(this, arguments)) {
+            this.started = false;
             this.dragging = false;
+            this.start = null;
+            this.last = null;
             deactivated = true;
         }
         return deactivated;