Fix cyclic messages support in generator. Beginnings of test.

Update issue 130
Status: Started

tests/cyclic_messages/cyclic.proto

@@ -0,0 +1,25 @@
+// Test structures with cyclic references.
+// These can only be handled in pointer/callback mode,
+// see associated .options files.
+
+message TreeNode
+{
+    optional int32 leaf = 1;
+    optional TreeNode left = 2;
+    optional TreeNode right = 3;
+}
+
+message Dictionary
+{
+    repeated KeyValuePair dictItem = 1;
+}
+
+message KeyValuePair
+{
+    required string key = 1;
+    optional string stringValue = 2;
+    optional int32 intValue = 3;
+    optional Dictionary dictValue = 4;
+    optional TreeNode treeValue = 5;
+}
+