today's changes

I have undone the bogosity of creating symlinks in the source directory.
That never should have been done, for at least two reasons.  That happened
along the way as I was making trivfs install its server stub headers
publically and #include them in trivfs.h, so that prototypes for the server
functions are in scope for both trivfs itself and programs that override
its stubs.  This required moving the priv.h goop into trivfs.h itself so as
not to need the import priv.h in the stub headers that are now public.  But
that stuff was not really all that private anyway.

I would like to do the same with netfs and diskfs as well.  Doing it for
trivfs caught several long-standing bugs (as well as some more recent 64
bit problems) in old definitions that had never been properly type-checked 
(mostly unused stubs, but still).