* In the case where an incremental table cannot be fully abolished
right away, and needs its space reclaimed later when it is safe, a
core dump was happening because of double use of pointers in
Variant subgoal frames. The problem was in freeing ALN lists, and
is fixed.
* In addition, it turned out that incremental tables were not being
properly invalidated when their space reclamation is delayed, so I
put a call to the invalidation function in those branches of the
code.
* Also, added a simple test that elicits the above conditions.
