Check highlight option in mouseover() instead of highlight().

This allow external methods to control the highlight status, just as it is possible to set isSelectable to false, and control the selection status from external methods.
Effectively, mouseover() and mouseout() no long call the highlight() and clearEffects() methods if the highlight option is false. Also, the highlight() method now highlights the area, regardless of the highlight option.
See jamietre#190.

src/areadata.js

@@ -244,9 +244,7 @@
 
         highlight: function (options) {
             var o = this.owner;
-            if (this.effectiveOptions().highlight) {
-                o.graphics.addShapeGroup(this, "highlight",options);
-            }
+            o.graphics.addShapeGroup(this, "highlight",options);
             o.setHighlightId(this.areaId);
             this.changeState('highlight', true);
         },

src/mapdata.js

@@ -156,6 +156,11 @@
         if (me.currentAreaId === ar.areaId) {
             return;
         }
+
+        if (!ar.effectiveOptions().highlight) {
+            return;
+        }
+
         if (me.highlightId !== ar.areaId) {
             me.clearEffects();
 
@@ -201,6 +206,10 @@
             return;
         }
 
+        if (!ar.effectiveOptions().highlight) {
+            return;
+        }
+
         newArea=me.getDataForArea(e.relatedTarget);
 
         if (newArea === ar) {