move Migration support into OpenSim.Data, because it

really turned out to be small enough to not need it's own
assembly

OpenSim/Data/Migration.cs

@@ -34,7 +34,7 @@ using System.Reflection;
 using System.Text.RegularExpressions;
 using log4net;
 
-namespace OpenSim.Data.Migrations
+namespace OpenSim.Data
 {
     /// <summary> 
     ///