Deserialize annotations on class members

Make 'Callable' message of descriptors.proto extensible, extend it in
java_descriptors.proto with a JVM signature of the member. This is needed in
order for annotation deserializer to find out which member in the compiled
bytecode corresponds to which descriptor in the hierarchy.

Create a new module 'serialization.java' containing everything related to
Java-specific serialization of descriptors.

Add an extension point to DescriptorSerializer, allowing to perform
platform-specific serialization on a callable

compiler/frontend.java/serialization.java/src/java_descriptors.proto

@@ -0,0 +1,26 @@
+/*
+ * Copyright 2010-2013 JetBrains s.r.o.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.jetbrains.jet.descriptors.serialization;
+
+import "compiler/frontend/serialization/src/descriptors.proto";
+
+option java_outer_classname = "JavaProtoBuf";
+option optimize_for = LITE_RUNTIME;
+
+extend Callable {
+  optional string java_signature = 100;
+}