Update Run/Halt Debug State Machine. (#629)

* Update Run/Halt Debug State Machine.

Bring the diagram up-to-date with what the spec says. Added abstract
command error states when an abstract command is issued while running.
Removed individual abstract commands since it got to be too messy.

In response to thread on mailing list subject:"A query regarding the
State Machine".

* Refine diagram a bit.

* Note that the diagram is not exhaustive.