add key 'h' for cmd-until-here: continue until the current line

[cranechu]

Hi,

Here is the code for issue #116.

Thanks,
-Crane

[rocky]

Ok. Let's try it - nothing ventured, nothing gained.

[rocky]

By the way, I note debuggers that don't support "unitl x" will need to register that fact. I'll probably do this later.