Termination behaviour of &, &&, |, ||, /

[AndreVanDelft]

Normally n-ary nodes are deactivated when they have no children any more.
This is done in line 451 of ContinuationHandler.scala:

if (node.children.isEmpty) insertDeactivation(node, null)

However, for operators &, &&, |, ||, / part of the children may be optional:
activated after a break?, and no atomic actions have yet happened therein.

The deactivation test should only take the set of other nodes into account;
when this test is matched the optionally activated children should be removed.

The code should have clear comments that explains what is being done.