Make compatible with V8 3.28.23, fixes #99
IdleNotification is on Isolate now
GetConstructor method was removed, use GetConstructorName and instanciate on our own
Add test on constructor get-accessor.
Don't explicitly indicate constructor, let V8 figure out

The GetConstructor function was removed from v8::Object which
would require some work to find out.  But V8 can do it
internally, so just leave it to V8 :)