added unit test to EncoderDecoderTestGwt which demonstrates a problem with missing @class attribute in json when using an encoder of a concrete implementation instead of a super class. This leads to exceptions when decoding the created json to java object with jackson 2.3.2 on server side in a spring mvc controller
fix for issue #212. JsonTypeInfo and JsonSubTypes annotations must not be searched on current class only.

Theses annotations must be searched on the current class, on all parent classes and interfaces.
Merge pull request #217 from bcourtine/issue212

fix for issue #212.