dip1008 compliant

[skoppe]

During some asynchronous cleanup we sometimes have to take a hold of exception to rethrow them later, but this interferes with dip1008 scope assumptions.

For refcounted exception we should be able to incr/decr the refcount.

Statically or stack allocated ones are still an issue. We would need to clone them. But besides there not being a clone function on exceptions, it is likely hard to detect those exceptions.