Re-evaluate marked regs when they are invalidated.
Allow making heads re_evaluate-d.
If something becomes re_evaluate-d, we should evaluate it immediately.
Copy and clear triggers in Parameters::recalc( ).
Add an implementation of trigger_on.
Fix parsing error.
Allow Og debug level.
Rewrite initial setting of re_evaluate.
Write out re_evaluate nodes as outlined in yellow.
Obtain triggers more cleanly.
Create triggers for each of the branch means.
Remove P.recalc_all().