onheap command

I have just added a onheap command. It let one see the number of objects on the heap. I guess it have to be modified so one can get the output into a file, but this may be a common command task.

From my view it looks like we have to look at the numbers of objects like String.

Other things that I could add is a selected output taken from an input pattern, like "org.jnode.*", "awt" etc.

Regards,
Martin