Instead of trying to be clever and make an 'educated guess' as to where
the flow of control may go next, simple do the more naive, yet correct,
approach of setting a breakpoint everywhere we can in the function and
seeing where we end up. On top of this we were already setting a
breakpoint at the return address and deferred functions, so that remains
the same.

This removes a lot of gnarly, hard to maintain code and takes all the
guesswork out of this command.

Fixes #281