Return (new) values in atomic_t::add() and ::sub()

We now make real use of these.

Signed-off-by: Matt Benjamin <matt@linuxbox.com>
Another (hopefully temporary) msgref change.

It now appears that we MUST currently request delivery
receipts on all messages in a chain.

It also appears that a reliable algorithm for disposing
sender-side messages without delivery receipts (at least
in the common case) is necessary to get full performance
with one-way.  We're still trying to convince Eyal of
that.

Signed-off-by: Matt Benjamin <matt@linuxbox.com>
Merge branch 'xio-firefly-cmake-multi-ref' of https://github.com/linuxbox2/linuxbox-ceph into xio-firefly-cmake-multi-ref

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

Conflicts:
	src/msg/XioMsg.h