nsqd: improve in flight pqueue remove test

this actually asserts that the message removed was the one
we asked for (this is what was broken)
nsqd: fix inflight pqueue remove 'double Pop'
nsqd: fix missing lock around client map
nsqd: log client IDENTIFY
Merge pull request #390 from mreiferson/stuck_in_flight_390

nsqd: messages stuck in-flight