Use v8::Signature, and other problems with Object example

[paulharris]

Problem 1)
You call ObjectWrap::Unwrap, which grabs the original pointer from This().
Shouldn't it be using Holder() and not This() ?

Problem 2)
Your 06_objects example is missing a critical part of the example - v8::Signature for type safety.
see line 489 here:
https://github.com/laverdet/node-fibers/blob/master/src/fibers.cc

Problem 3)
You create a Persistent global handle for constructor, and then do nothing with it.
This example also won't work for other v8 embedders who might be using v8 in multiple Isolates and threads.

Instead, it should be a plain Local handle (no global constructor handle), and use the Signature technique to ensure type safety.

[markate]

well done