Upgrade nunit.framework.dll to version 2.5.9. Fix up tests appropriately.

This version removes the NUnit.Framework.SyntaxHelpers namespace, so any modules with their own tests will need to delete this using statement.

OpenSim/Tests/Common/DoubleToleranceConstraint.cs

@@ -27,6 +27,7 @@
 
 using System;
 using NUnit.Framework;
+using NUnit.Framework.Constraints;
 
 namespace OpenSim.Tests.Common
 {

OpenSim/Tests/Common/TestHelper.cs

@@ -27,11 +27,10 @@
 
 using System;
 using System.Diagnostics;
+using NUnit.Framework;
 
 namespace OpenSim.Tests.Common
 {
-    public delegate void TestDelegate();
-
     public class TestHelper
     {
         public static bool AssertThisDelegateCausesArgumentException(TestDelegate d)

OpenSim/Tests/Common/VectorToleranceConstraint.cs

@@ -28,6 +28,7 @@
 using System;
 using OpenMetaverse;
 using NUnit.Framework;
+using NUnit.Framework.Constraints;
 
 namespace OpenSim.Tests.Common
 {