Unreachable instances

If a generation #0 heap snapshot has been performed, it is possible that there are instances left on the heap that are not reachable from any root. The reason for this is that the garbage collector does not make a full reachability analysis when performing a generation #0 collection and does not know whether some instances are reachable or not.

The number of unreachable instances of each type is presented when showing heap utilization information. This number can be used to analyze how well the garbage collected heap is utilized.