added better db migration support than what Subsonic provides out of the box.

Migrator.net/Migrator/DuplicatedVersionException.cs

@@ -0,0 +1,26 @@
+#region License
+//The contents of this file are subject to the Mozilla Public License
+//Version 1.1 (the "License"); you may not use this file except in
+//compliance with the License. You may obtain a copy of the License at
+//http://www.mozilla.org/MPL/
+//Software distributed under the License is distributed on an "AS IS"
+//basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See the
+//License for the specific language governing rights and limitations
+//under the License.
+#endregion
+
+using System;
+
+namespace Migrator
+{
+	/// <summary>
+	/// Exception thrown when a migration number is not unique.
+	/// </summary>
+	public class DuplicatedVersionException : Exception
+	{
+		public DuplicatedVersionException(long version)
+			: base(String.Format("Migration version #{0} is duplicated", version))
+		{
+		}
+	}
+}