Gson should support Wildcard types

[GoogleCodeExporter]

We should add support for Wildcard fields where it is "extending" some
object.  For example:

public class Foo {
  private static final List<? extends Number> EMPTY_LIST = Collections.
  private final List<? extends Number> listOfNumbers;

  public Foo() {
    this(null);
  }

  public Foo(List<? extends Number> list) {
    this.listOfNumbers = list;
  }
}

Original issue reported on code.google.com by joel.leitch@gmail.com on 28 Aug 2008 at 8:14