Addded GetSubTypeDefinitions method.

That's like a routine we had in the old MD dom - it's used for example
for finding all exceptions in an assembly.

ICSharpCode.NRefactory/TypeSystem/ExtensionMethods.cs

@@ -252,6 +252,19 @@ namespace ICSharpCode.NRefactory.TypeSystem
 					.Concat (type.GetMethods (context, filter).SafeCast<IMethod, IMember> ())
 					.Concat (type.GetEvents (context, filter).SafeCast<IEvent, IMember> ());
 		}
-		#endregion	
+		#endregion
+		
+		#region GetSubTypeDefinitions
+		/// <summary>
+		/// Gets all sub type definitions defined in a context.
+		/// </summary>
+		public static IEnumerable<ITypeDefinition> GetSubTypeDefinitions (this IType baseType, ITypeResolveContext context)
+		{
+			foreach (var contextType in context.GetAllClasses ()) {
+				if (contextType.IsDerivedFrom (baseType, context))
+					yield return contextType;
+			}
+		}
+		#endregion
 	}
 }

ICSharpCode.NRefactory/TypeSystem/IAnnotatable.cs

@@ -9,7 +9,7 @@ using System.Threading;
 namespace ICSharpCode.NRefactory
 {
 	/// <summary>
-	/// Provides an interface to handle annotations in an objectj
+	/// Provides an interface to handle annotations in an object.
 	/// </summary>
 	public interface IAnnotatable
 	{