JOL object header information

[Rafael Winterhalter]

First of all, thanks for the hint to the ServiceabiltyAgent, did not even
know HotSpot had this.

If this is considered feasible: One could play similar tricks and
self-attach an agent via tools.jar and always print the correct instance
size via the Instrumentation API and only print the estimated size if this
is impossible? I would be more than happy to implement the feature, I just
did something similar for a test suite that required an agent. Most people
run JOL on an OpenJDK VM anyways?

The only concern is that this would break with Jigsaw but this is also true
for the proposal to integrating the ServiceabiltyAgent.

Regards, Rafael