Fix multiple finalizers running during a single GC.
Fix multiple finalizers running during a single GC.

The finalizer lists were being mismanaged, causing completed finalizers
to be run multiple times.

rvedam/Mezzano,froggey/Mezzano,varjagg/Mezzano,froggey/Mezzano,varjagg/Mezzano,rvedam/Mezzano