Make Object and derived classes use SharedPtr with the Original mapping

[bernardnormier]

This PR changes ObjectPtr to be a SharedPtr with the Original mapping. It's the first step in making the same Ice::Object the common Object base class for the Original and New mappings.

You'll notice:

• there are few C++ updates, especially test updates, which is good as it shows this update is largely source compatible
• the updates are mostly related to "this" sharing
• there was no update to PHP and Ruby, and minimal updates to Python
• unfortunately Objective-C required more updates as it was overwriting IceUtil::Shared __incRef and __decRef.

[externl]

Looks good