Per-value metatables would be great for threads

[Dirk Laurie <dirk.laurie@...>]

Was there near-universal acclaim for per-value metatables,
or am I just remembering what I like to? Anyway, pointing out
one more advantage can't hurt :-)

When a coroutine goes dead, there is often some finalizing to do.
Setting a return hook in order to call a finalizer looks kludgy.
The neat way is a __gc metamethod.