Closes #1490. Add comment to make it clear that callers of createPopup must not call destroy on returned popups but rather use the feature.destroyPopup method.

git-svn-id: http://svn.openlayers.org/trunk/openlayers@6820 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Feature.js

@@ -161,6 +161,10 @@ OpenLayers.Feature = OpenLayers.Class({
      *  
      *  If no 'lonlat' is set, returns null. 
      *  If no this.marker has been created, no anchor is sent.
+     *
+     *  Note - the returned popup object is 'owned' by the feature, so you
+     *      cannot use the popup's destroy method to discard the popup.
+     *      Instead, you must use the feature's destroyPopup
      * 
      *  Note - this.popup is set to return value
      *