Fix 'allow unresolved' for at least two list cases

lists did not respond well to cases where only some of their
elements were resolved or even when none of them were resolved
but one of their object identities happened to change. Previously
this would throw a nasty 'bug or broken' exception so it seems
unlikely to have unintended side effects.
isolate test for allowing unresolved list elements
Merge pull request #180 from tea-dragon/master

Fix 'allow unresolved' for at least two list cases