common/cmdparse: no need to use (and leak to) the heap

Signed-off-by: Sage Weil <sage@inktank.com>
messages/MMonSync: initialize crc in ctor

Signed-off-by: Sage Weil <sage@inktank.com>
mon: shut down Paxos on shutdown

This cleans up the completions for any paxos waiters.

Signed-off-by: Sage Weil <sage@inktank.com>
mon: add is_shutdown() state helper/accessor

Signed-off-by: Sage Weil <sage@inktank.com>
mon/PaxosService: discard messages during shutdown

Signed-off-by: Sage Weil <sage@inktank.com>