Add a conditional debug macro
Leave a message if a test crashes
Better control of status for newly spawned processes

When a process is spawned it waits for the scheduler to assign an LID and
the next signal should be a simple continue. If, however, a child process
is spawned, the poll message for unhandled messages was sent before that.
This patch makes explicit which message should arrive first.
More clarified non-dependencies
Receive statements may have guards

If the guard is not taken into account we may assume that a receive statement
is unblocked when it in fact it is not.
Monitor messages may need to be added retroactively (just like link)

When there is a send or exit, evidence should be gathered about whether
messages could be sent to processes that no longer exist. This evidence
now includes information about monitors.