I've just committed a large patch which allows the SourceWindow to
handle processes with multiple threads. That is, it properly blocks and
unblocks them, and if the source code is available, should display the
source from each thread and highlight the appropriate lines properly.

Thanks to Tom's idea, it uses a TreeView widget to list each thread and
their respective frames on the call stack.

I'm pretty sure that bugs exist! If you have some free time and want to
check it out, I've attached an example test program. Please assign any
breakage to me.

- Mike