minor: add method doc to DAMap.ValidateKey()

OpenSim/Framework/DAMap.cs

@@ -168,6 +168,10 @@ namespace OpenSim.Framework
             }
         }
 
+        /// <summary>
+        /// Validate the key used for storing separate data stores.
+        /// </summary>
+        /// <param name='key'></param>
         private static void ValidateKey(string key)
         {
             if (key.Length < MIN_STORE_NAME_LENGTH)