object graph recursion with polymorphism using GraphAdapterBuilder and RuntimeTypeAdapterFactory

```
When used in conjunction, the classes GraphAdapterBuilder and
RuntimeTypeAdapterFactory produce an IllegalStateException "Unexpected
recursive call to read()" on de-serialization.

When used separately, GraphAdapterBuilder can serialize and de-serialize
circular references, and RuntimeTypeAdapterFactory can tackle classes involving
polymorphism. When used together, serialization succeeds but de-serialization
fails.

What steps will reproduce the problem?
Add the attached source files to a project, and execute the JUnit tests.

What is the expected output? What do you see instead?
All tests (testRecursive, testPolymorphic and testPolymorphicRecursive) in the
attached source should pass. Instead, testPolymorphicRecursive fails with an
exception.

What version of the product are you using? On what operating system?
Gson 2.2.4
RuntimeTypeAdapterFactory from
https://code.google.com/p/google-gson/source/browse/trunk/extras/src/main/java/c
om/google/gson/typeadapters/RuntimeTypeAdapterFactory.java
GraphAdapterBuilder from
https://code.google.com/p/google-gson/source/browse/trunk/extras/src/main/java/c
om/google/gson/graph/GraphAdapterBuilder.java with the changes made as
suggested in https://code.google.com/p/google-gson/issues/detail?id=137#c12

```

Original issue reported on code.google.com by `huny...@gmail.com` on 17 Nov 2013 at 2:38

Attachments:
- [gson-polymorphic-recursive.zip](https://storage.googleapis.com/google-code-attachments/google-gson/issue-542/comment-0/gson-polymorphic-recursive.zip)