add accessor for pivot accessor

Author: taylorotwell

src/Illuminate/Database/Eloquent/Relations/BelongsToMany.php

@@ -952,4 +952,14 @@ public function getRelationName()
     {
         return $this->relationName;
     }
+
+    /**
+     * Get the name of the pivot accessor for this relationship.
+     *
+     * @return string
+     */
+    public function getPivotAccessor()
+    {
+        return $this->accessor;
+    }
 }