[644507] Don't use nested type cache until declaring type is setup.

mcs/mcs/import.cs

@@ -652,7 +652,25 @@ namespace Mono.CSharp
 
 			import_cache.Add (type, spec);
 
-			if (kind == MemberKind.Interface)
+			//
+			// Two stage setup as the base type can be inflated declaring type
+			//
+			if (declaringType == null)
+				ImportTypeBase (spec, type);
+
+			return spec;
+		}
+
+		public void ImportTypeBase (Type type)
+		{
+			TypeSpec spec = import_cache[type];
+			if (spec != null)
+				ImportTypeBase (spec, type);
+		}
+
+		void ImportTypeBase (TypeSpec spec, Type type)
+		{
+			if (spec.Kind == MemberKind.Interface)
 				spec.BaseType = TypeManager.object_type;
 			else if (type.BaseType != null)
 				spec.BaseType = CreateType (type.BaseType);
@@ -663,8 +681,6 @@ namespace Mono.CSharp
 					spec.AddInterface (CreateType (iface));
 				}
 			}
-
-			return spec;
 		}
 
 		TypeParameterSpec CreateTypeParameter (Type type, TypeSpec declaringType)
@@ -1353,7 +1369,7 @@ namespace Mono.CSharp
 
 					break;
 				case MemberTypes.NestedType:
-					// Already done
+					meta_import.ImportTypeBase ((Type) member);
 					continue;
 				default:
 					throw new NotImplementedException (member.ToString ());

mcs/tests/gtest-451-lib.cs

+// Compiler options: -t:library
+
+using System;
+
+public class A<T> where T : new ()
+{
+	public T Value = new T ();
+	
+	public class N1 : A<N2>
+	{
+	}
+	
+	public class N2
+	{
+		public int Foo ()
+		{
+			return 0;
+		}
+	}
+}
\ No newline at end of file

mcs/tests/gtest-451.cs

+// Compiler options: -r:gtest-451-lib.dll
+
+public class Test
+{
+	public static int Main ()
+	{
+		var a = new A<int>.N1 ();
+		return a.Value.Foo ();
+	}
+}