Clear cached mousedown/up positions used for distinguishing between

drag and click in feature handler after a click event.

Fixes #856

lib/OpenLayers/Handler/Feature.js

@@ -353,6 +353,11 @@ OpenLayers.Handler.Feature = OpenLayers.Class(OpenLayers.Handler, {
                 if(dpx <= this.clickTolerance) {
                     this.callback(key, args);
                 }
+                // we're done with this set of events now: clear the cached
+                // positions so we can't trip over them later (this can occur
+                // if one of the up/down events gets eaten before it gets to us
+                // but we still get the click)
+                this.up = this.down = null;
             } else {
                 this.callback(key, args);
             }