KT-499 allow class object in static inner classes

like this:

===
class A {
    class object {
        class B {
            class object { }
        }
    }
}
===

compiler/frontend/src/org/jetbrains/jet/lang/descriptors/MutableClassDescriptor.java

@@ -61,7 +61,7 @@ public class MutableClassDescriptor extends MutableDeclarationDescriptor impleme
     @Override
     public ClassObjectStatus setClassObjectDescriptor(@NotNull MutableClassDescriptor classObjectDescriptor) {
         if (this.classObjectDescriptor != null) return ClassObjectStatus.DUPLICATE;
-        if (!(this.getContainingDeclaration() instanceof NamespaceDescriptor)) {
+        if (!isStatic(this.getContainingDeclaration())) {
             return ClassObjectStatus.NOT_ALLOWED;
         }
         assert classObjectDescriptor.getKind() == ClassKind.OBJECT;
@@ -69,6 +69,17 @@ public class MutableClassDescriptor extends MutableDeclarationDescriptor impleme
         return ClassObjectStatus.OK;
     }
 
+    private static boolean isStatic(DeclarationDescriptor declarationDescriptor) {
+        if (declarationDescriptor instanceof NamespaceDescriptor) {
+            return true;
+        } else if (declarationDescriptor instanceof ClassDescriptor) {
+            ClassDescriptor classDescriptor = (ClassDescriptor) declarationDescriptor;
+            return classDescriptor.getKind() == ClassKind.OBJECT || classDescriptor.getKind() == ClassKind.ENUM_CLASS;
+        } else {
+            return false;
+        }
+    }
+
     @Nullable
     public MutableClassDescriptor getClassObjectDescriptor() {
         return classObjectDescriptor;

compiler/testData/checkerWithErrorTypes/quick/InnerClassClassObject.jet

@@ -5,3 +5,16 @@ class A {
         <!CLASS_OBJECT_NOT_ALLOWED!>class object { }<!>
     }
 }
+
+class B {
+    class object {
+        class B {
+            class object {
+                class C {
+                    class object { }
+                }
+            }
+        }
+    }
+}
+