Mantis#1591. Thank you graciously, Sempuki for a patch that:

Currently module loading is done ad-hoc. I propose creating a simple 
loader class that leverages Mono.Addins (and perhaps the new .NET 
addins when they become available in mono). Attached is a basic 
patch for review that compiles into HEAD, but doesn't yet replace 
any existing ad-hoc loaders.

OpenSim/ApplicationPlugins/Rest/RestPlugin.cs

@@ -188,6 +188,17 @@ namespace OpenSim.ApplicationPlugins.Rest
 
 
         #region methods
+        // TODO: required by IPlugin, but likely not at all right
+        string m_version = "0.0";
+
+        public string Version { get { return m_version; } }
+
+        public void Initialise() 
+        { 
+            m_log.Info("[RESTPLUGIN]: " + Name + " cannot be default-initialized!");
+            throw new PluginNotInitialisedException (Name);
+        }
+
         /// <summary>
         /// This method is called by OpenSimMain immediately after loading the
         /// plugin and after basic server setup,  but before running any server commands.
@@ -357,6 +368,11 @@ namespace OpenSim.ApplicationPlugins.Rest
             _agents   = null;
         }
 
+        public virtual void Dispose()
+        {
+            Close();
+        }
+
         /// <summary>
         /// Return a failure message.
         /// </summary>