Breakpoint handling is now more straightforward. The interface between the
instrumentation (breakpoints) and the monitor is now materialized by an event
manager that can be itself checkpointed.

Scenarios weren't working correctly. Checkpointing has further been stabilized.
This is one of the biggest commit of this project and its inception has been
slow and painful. This is the result of fiddling and making things eventually
work by accident. To make things work, some other things were done in parallel
and now it is hard (though not impossible) to make beautiful meaningful small
commits. So we'll get one monolithic commit. Tough life.