Tweaks to search order in the indexer.

* The set indexer now respects locks.
* The current object is searched before the prototype in both get and set indexers, falling back on the metamethods if necessary.
* New ctor for MondValue to attach a MondState to the underlying Object.
* Fix possible NullReferenceException in Object.cs if TryDispatch was called but it was never given a valid MondState.