Implement getNamespace() for deserialized scope

DescriptorFinder now can find packages, pull the method up from
AbstractDescriptorFinder class

compiler/frontend.java/src/org/jetbrains/jet/lang/resolve/java/resolver/DeserializedDescriptorResolver.java

@@ -66,6 +66,12 @@ public final class DeserializedDescriptorResolver {
         public ClassDescriptor findClass(@NotNull ClassId classId) {
             return javaClassResolver.resolveClass(kotlinFqNameToJavaFqName(classId.asSingleFqName()));
         }
+
+        @Nullable
+        @Override
+        public NamespaceDescriptor findPackage(@NotNull FqName name) {
+            return javaNamespaceResolver.resolveNamespace(name);
+        }
     };
 
     @Inject