adding a feature.modified property, making the ModifyFeature control set it and the WFST format check for it so only modified attributes and a modified geometry need to be included in an Update transaction. r=bartvde (closes #3400)

git-svn-id: http://svn.openlayers.org/trunk/openlayers@12149 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Feature/Vector.js

@@ -81,6 +81,42 @@ OpenLayers.Feature.Vector = OpenLayers.Class(OpenLayers.Feature, {
      * {String} rendering intent currently being used
      */
     renderIntent: "default",
+    
+    /**
+     * APIProperty: modified
+     * {Object} An object with the originals of the geometry and attributes of
+     * the feature, if they were changed. Currently this property is only read
+     * by <OpenLayers.Format.WFST.v1>, and written by
+     * <OpenLayers.Control.ModifyFeature>, which sets the geometry property.
+     * Applications can set the originals of modified attributes in the
+     * attributes property. Note that applications have to check if this
+     * object and the attributes property is already created before using it.
+     * After a change made with ModifyFeature, this object could look like
+     *
+     * (code)
+     * {
+     *     geometry: >Object
+     * }
+     * (end)
+     *
+     * When an application has made changes to feature attributes, it could
+     * have set the attributes to something like this:
+     *
+     * (code)
+     * {
+     *     attributes: {
+     *         myAttribute: "original"
+     *     }
+     * }
+     * (end)
+     *
+     * Note that <OpenLayers.Format.WFST.v1> only checks for truthy values in
+     * *modified.geometry* and the attribute names in *modified.attributes*,
+     * but it is recommended to set the original values (and not just true) as
+     * attribute value, so applications could use this information to undo
+     * changes.
+     */
+    modified: null,
 
     /** 
      * Constructor: OpenLayers.Feature.Vector