Change simple_dispatcher to always reply.

This appears to mean that the reported times at either endpoint
reflect .5*<one-way-time-elapsed>, and of course it is printed
currently for the count mod 2048.

Note that this is now incorrect for XioMessenger, at least without
other changes.  I will probably create a new dispatcher subclass
for XioMessenger testing.

Signed-off-by: Matt Benjamin <matt@linuxbox.com>
Add n_msgs and n_dsize params to simple_client.

Also clean up simple_dispatcher msg type behavior, and
print better info at startup, shutdown.

Signed-off-by: Matt Benjamin <matt@linuxbox.com>
Add n_msgs and n_dsize params to xio_client.

Also use new XioDispatcher in both xio_client and xio_server.
The two test driver dispatchers now differ in their use of
completions and mechanism for re-sending dispatched messages
(which keeps messages flowing with a fixed initial depth).

Signed-off-by: Matt Benjamin <matt@linuxbox.com>