Add m_syncRoot lock to MapAndArray.ContainsKey(), as discussed with jhurliman

Though this is actually thread-safe on .net 4.0 and mono today, the .net sdk states that Dictionary instance members are not guaranteed thread-safe

OpenSim/Framework/MapAndArray.cs

@@ -1,4 +1,4 @@
-/*
+/*
  * Copyright (c) Contributors, http://opensimulator.org/
  * See CONTRIBUTORS.TXT for a full list of copyright holders.
  *
@@ -131,7 +131,8 @@ namespace OpenSim.Framework
         /// <returns>True if the key was found, otherwise false</returns>
         public bool ContainsKey(TKey key)
         {
-            return m_dict.ContainsKey(key);
+            lock (m_syncRoot)
+                return m_dict.ContainsKey(key);
         }
 
         /// <summary>