Object Versioning: fixed duplication issue in enumerate-trap
Object Versioning: write __objectID also into virtualTarget

as when __objectID is not configurable and not writable, the proxy spec
requires the proxy to return a value consistently to the proxy's actual
target object (which we otherwise not use as our proxies are virtual)
Object Versioning: fix __proto__-issue in set-trap

__proto__ should not be written into the regular target object, but
only affect the __protoID of it. basically, this was just a missing
'return true'.
Object Versioning: init() only when versioning not yet active
Object Versioning: only proxy prototype props that aren't proxied
Object Versioning: only proxy in actual lively classes benchmark