1. namespace class should not be accessible from Kotlin despite the fact we don't have kotlin class descriptor for it.

2. testdata is corrected due to the fact frontend has wrong qualified name in trace for root namespace

compiler/frontend.java/src/org/jetbrains/jet/lang/resolve/java/JavaPackageScope.java

@@ -77,6 +77,7 @@ public class JavaPackageScope extends JetScopeImpl {
             final PsiPackage javaPackage = semanticServices.getDescriptorResolver().findPackage(packageFQN);
 
             if (javaPackage != null) {
+                boolean isKotlinNamespace = semanticServices.getKotlinNamespaceDescriptor(javaPackage.getQualifiedName()) != null;
                 final JavaDescriptorResolver descriptorResolver = semanticServices.getDescriptorResolver();
 
                 for (PsiPackage psiSubPackage : javaPackage.getSubPackages()) {
@@ -84,6 +85,8 @@ public class JavaPackageScope extends JetScopeImpl {
                 }
 
                 for (PsiClass psiClass : javaPackage.getClasses()) {
+                    if (isKotlinNamespace && "namespace".equals(psiClass.getName())) continue;
+
                     // If this is a Kotlin class, we have already taken it through a containing namespace descriptor
                     ClassDescriptor kotlinClassDescriptor = semanticServices.getKotlinClassDescriptor(psiClass.getQualifiedName());
                     if (kotlinClassDescriptor != null) {

idea/testData/completion/basic/ExtendClassName.kt

@@ -1,3 +1,5 @@
+namespace foo
+
 open class MySecondClass() {
 }