Add a panDuration property to the map. This allows for a workaround for

VirtualEarth panning with markers which causes drift, using the 'novibrate'
example. Tests continue to pass. r=me (Closes #1947)


git-svn-id: http://svn.openlayers.org/trunk/openlayers@9130 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Map.js

@@ -384,6 +384,15 @@ OpenLayers.Map = OpenLayers.Class({
      */
     panMethod: OpenLayers.Easing.Expo.easeOut,
     
+    /**
+     * Property: panDuration
+     * {Integer} The number of steps to be passed to the
+     * OpenLayers.Tween.start() method when the map is
+     * panned.
+     * Default is 50.
+     */
+    panDuration: 50,
+    
     /**
      * Property: paddingForPopups
      * {<OpenLayers.Bounds>} Outside margin of the popup. Used to prevent 
@@ -1472,7 +1481,7 @@ OpenLayers.Map = OpenLayers.Class({
                 lon: lonlat.lon,
                 lat: lonlat.lat
             };
-            this.panTween.start(from, to, 50, {
+            this.panTween.start(from, to, this.panDuration, {
                 callbacks: {
                     start: OpenLayers.Function.bind(function(lonlat) {
                         this.events.triggerEvent("movestart");