The external interfaces chapter has a section where caching on
additional opaque handles is proposed. The current draft adds groups
and datatypes. The one to be released soon adds persistant requests.
There is a note that we need to decide which other handles to add.
The only constraint is that we don't want to include handles that are
light weight (such as regular requests) where the overhead would be
noticable. I think that file handles are ok. Thus, I will add file
handles to the list unless someone objects.
Steve