Shared objects are built on top of `tao_shared_data_t` instances which
provide a mechanism for r/w locking the resource.  The code for
finalizing shared resources is simpler because we can assume that
the mutex associated to shared data is always owned for a short period.
This will also simplifies getting images from a remote camera: semaphores
will no longer be needed (code compiles but is broken for now in that
respect).

Most functions return a `tao_status_t` to represent success, error or
timeout.  This simplifies and unifies calls to functions with a duration
limit.  This makes the code more clear about the intention:
`foo(...) == TAO_OK` is much better than `foo(...) == 0` or, worse,
`!foo(...)`.