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/Data/AssetDataBase.cs

@@ -42,5 +42,6 @@ namespace OpenSim.Data
         public abstract string Name { get; }
         public abstract void Initialise(string connect);
         public abstract void Initialise();
+        public abstract void Dispose();
     }
 }

OpenSim/Data/MSSQL/MSSQLAssetData.cs

@@ -218,6 +218,8 @@ namespace OpenSim.Data.MSSQL
 
         #region IPlugin Members
 
+        override public void Dispose() { }
+
         /// <summary>
         /// <para>Initialises asset interface</para>
         /// <para>

OpenSim/Data/MySQL/MySQLAssetData.cs

@@ -39,7 +39,7 @@ namespace OpenSim.Data.MySQL
     /// <summary>
     /// A MySQL Interface for the Asset Server
     /// </summary>
-    internal class MySQLAssetData : AssetDataBase, IPlugin
+    internal class MySQLAssetData : AssetDataBase
     {
         private static readonly ILog m_log = LogManager.GetLogger(MethodBase.GetCurrentMethod().DeclaringType);
 
@@ -109,6 +109,8 @@ namespace OpenSim.Data.MySQL
 
         }
 
+        override public void Dispose() { }
+
         #region IAssetProvider Members
 
         /// <summary>

OpenSim/Data/NHibernate/NHibernateAssetData.cs

@@ -43,7 +43,7 @@ namespace OpenSim.Data.NHibernate
     /// <summary>
     /// A User storage interface for the DB4o database system
     /// </summary>
-    public class NHibernateAssetData : AssetDataBase, IDisposable
+    public class NHibernateAssetData : AssetDataBase
     {
         private static readonly ILog m_log = LogManager.GetLogger(MethodBase.GetCurrentMethod().DeclaringType);
 
@@ -51,6 +51,8 @@ namespace OpenSim.Data.NHibernate
         private ISessionFactory factory;
         private ISession session;
 
+        override public void Dispose() { }
+
         public override void Initialise()
         {
             Initialise("SQLiteDialect;SqliteClientDriver;URI=file:Asset.db,version=3");
@@ -173,9 +175,5 @@ namespace OpenSim.Data.NHibernate
             get { return "0.1"; }
         }
 
-        public void Dispose()
-        {
-
-        }
     }
 }

OpenSim/Data/SQLite/SQLiteAssetData.cs

@@ -56,6 +56,8 @@ namespace OpenSim.Data.SQLite
 
         private SqliteConnection m_conn;
 
+        override public void Dispose() { }
+
         /// <summary>
         /// <list type="bullet">
         /// <item>Initialises AssetData interface</item>