Garbage collector throwing during collection

[dsimcha]

== Quote from Sean Kelly (sean at invisibleduck.org)'s article
> I started on the rewrite, but it's a pretty big change so I'm
> considering trying out Leandro's GC instead.  It would require some work
> as well, but the code is cleaner and it already supports precise
> scanning, so it may be a better starting point.

What's the scope of said rewrite?