DescriptorFinder now can find class names in a package

This helps to get rid of "repeated class_name" field in Package protobuf
message. DescriptorFinder in resolve.java uses PSI to find all classes in a
package, and the finder for built-ins just reads .kotlin_class_names file

compiler/tests/org/jetbrains/jet/codegen/KotlinClassAnnotationTest.java

@@ -32,8 +32,10 @@ import org.jetbrains.jet.lang.descriptors.impl.NamespaceDescriptorImpl;
 import org.jetbrains.jet.lang.resolve.lazy.storage.LockBasedStorageManager;
 import org.jetbrains.jet.lang.resolve.name.FqName;
 import org.jetbrains.jet.lang.resolve.name.FqNameUnsafe;
+import org.jetbrains.jet.lang.resolve.name.Name;
 
 import java.io.IOException;
+import java.util.Collection;
 
 public class KotlinClassAnnotationTest extends CodegenTestCase {
     public static final FqName NAMESPACE_NAME = new FqName("test");
@@ -90,6 +92,12 @@ public class KotlinClassAnnotationTest extends CodegenTestCase {
             return namespace;
         }
 
+        @NotNull
+        @Override
+        public Collection<Name> getClassNames(@NotNull FqName packageName) {
+            throw new UnsupportedOperationException();
+        }
+
         @Override
         protected void classDescriptorCreated(@NotNull ClassDescriptor classDescriptor) {
         }