WARNING: BREAKING CHANGES FOR REGION MODULE DEVELOPMENT.

This cleans up Opensim's use of mono addins. In particular, the extension points /OpenSim/RegionModules and /OpenSim/WindModule moved from OpenSim.exe to OpenSim.Region.Framework.dll. From here on, developers of region modules should declare their dlls to be dependent on OpenSim.Region.Framework, starting with version 0.8.1
Additional changes:
- Addins version uniformly updated to 0.8.1. These numbers should be compatible with the release numbers or else it becomes very confusing.
- Mono addins directives moved from files addins.xml to embedded directives in the class and assembly declarations, to make it all consistent

OpenSim/Region/Framework/Interfaces/IWindModelPlugin.cs

@@ -33,8 +33,11 @@ using OpenSim.Framework;
 using OpenMetaverse;
 using OpenSim.Region.Framework.Scenes;
 
+using Mono.Addins;
+
 namespace OpenSim.Region.Framework.Interfaces
 {
+    [TypeExtensionPoint(Path = "/OpenSim/WindModule", NodeName = "WindModel")]
     public interface IWindModelPlugin : IPlugin
     {
         /// <summary>