Add support for circular references in data contracts

[apatenotre]

Hi!

First of all, thank you for your project.

It appears that circular references in datacontract objects are not well supported, and always lead to a StackOverflowException. This seems to be due to the way recursivity is handled while parsing objects in the MetaWCFBodyBuilder class.

Short example :

[DataContract]
public class CircularReferenceFirstObject
{
    [DataMember]
    public CircularReferenceSecondObject SecondObject { get; set; }
}

references

[DataContract]
public class CircularReferenceSecondObject
{
    [DataMember]
    public CircularReferenceFirstObject FirstObject { get; set; }
}

which references CircularReferenceFirstObject. StackOverflow is raised on first call.