attemp at implementing DllCanUnload now for dcompos

[James Hawkins]

Hey all,

It would really help me out if you could look over this patch and see
if I've incorrectly implemented ref-counting and DllCanUnloadNow for
dcompos.  I used suggestions from Rob and a sample implementation
written by him.  The only concern I have is that I'm not sure if all
of these classes are non-heap based.