server startup (sparse write avoidance doesn't happen until it is finished).
Added mutex to bitset functions, which were already being called from
multiple threads. Rewrote allocation map builder to request file
information in multiple chunks, to avoid uninterruptible wait and dynamic
memory allocation.
If the client makes a write that's out of range, by the time we get to
validate the message at the server end the client has already stuffed
the socket with data we can't use, so we have to flush it.
This patch also fixes a potential problem in the acceptance tests where
the error field was being returned as an array rather than a value.
trouble and into predictable cleanup functions (one for each of serve,
client & control contexts). We use 'fatal' to mean 'kill the thread' and
'error' to mean 'don't kill the thread', assuming some recovery action,
except I don't use error anywhere yet.
