Ensured same behavior of MetaClass#get[Declared]Fields() implementations.

* GWTClass.#get[Declared]Fields() and BuildMetaClass.#get[Declared]Fields() now behave the same like JavaReflectionClass.#get[Declared]Fields()
* Added a test case for building a class with access to inherited fields

Fixes https://issues.jboss.org/browse/ERRAI-640