RFR: 8271356: Modify jdb to treat an empty command as a repeat of the previous command [v5]

[Jakob Cornell]

> One section I'd like to see improved is the readability of the Problem section. The middle sentence is long winded and hard to read. Perhaps a bullet list would be better.

Right you are.  I've revised it to use bullet points, and while I've added a bit more detail to each they should be easier to follow.  If not, let me know and I can do some condensing.

Jakob