Fix Coercion fail message around Array and Object

[JooHyukKim]

resolves #3924

[cowtowncoder]

Ok. So, after reading, re-reading things, I am not sure this is quite the way to fix the problem.

The thing is that aside from "Scalar from Object" work-around needed for XML backend (failing for others including JSON), there is no coercion we would actually consider: we are just failing in general by calling ctxt.handleUnexpectedToken() -- but there we are passing getValueType(ctxt) which is wrong.

So I think test change is good, but the fix should be much simpler: I'll add a note to point it.

[cowtowncoder]

Ok so I can't attach code review comment in place, so this line:

return (String) ctxt.handleUnexpectedToken(getValueType(ctxt), p);

needs to be changed to, I think:

return (String) ctxt.handleUnexpectedToken(rawTargetType, p);

and that's the proper fix here.

Plus change to call ctxt.extractScalarFromObject(...) to also pass rawTargetType, not _valueClass.