Small stepping, which is stepping over sub-expressions (kinda), worked but was a little goofy. The mode was set on the client, passed over with control flow commands, placed on the execution context, then retrieved from there and used by those same flow commands. Removed the execution context part of it, since it was useless, and factored grabbing the offsets into the flow cmds where they belong instead of doing it all the time.
The run cmd also had some notion of small stepping, but you'll note it was never sent over the wire. Nuked that, since it never mattered anyway.
We had two similar-but-different functions for getting a notification from the VM about an exception. Cleaned that up by using the proper one for a thrown exception where appropriate, and moving the old one into a hook (like the other VM->debugger hooks) specifically for error messages.
There were multiple issues with flow control when exceptions occur. Fixed these by ditching the reliance on the exception thrown interrupt and introduce an exception handler interrupt, which indicates control is about to pass to a catch clause. This gives us much better insight into how execution is flowing and how we might need to adjust an in-flight stepping operation.