Got extension methods working for DynamicDocument. Exposes some new APIs publicly because they need to work with type finding and med trust, plus we need to expose these for MVC

src/Umbraco.Core/Dynamics/ExtensionMethodFinder.cs

@@ -11,13 +11,21 @@ namespace Umbraco.Core.Dynamics
 {
     internal static class ExtensionMethodFinder
     {
-		//TODO: This should be highly optimized!!! Calls to BuildManager.GetReferencedAssemblies() are really expensive!
+		
+
 
         private static List<MethodInfo> GetAllExtensionMethods(Type thisType, string name, int argumentCount, bool argsContainsThis)
         {
+			//only scan assemblies we know to contain extension methods (user assemblies)
+        	//var assembliesToScan = TypeFinder.GetAssembliesWithKnownExclusions();
+        	var assembliesToScan = new List<Assembly>()
+        		{
+        			Assembly.Load("Umbraco.Tests")
+        		};
+
             //get extension methods from runtime
             var candidates = (
-                from assembly in BuildManager.GetReferencedAssemblies().Cast<Assembly>()
+				from assembly in assembliesToScan
                 where assembly.IsDefined(typeof(ExtensionAttribute), false)
                 from type in assembly.GetTypes()
                 where (type.IsDefined(typeof(ExtensionAttribute), false)