After rebase: mget split to many mget and send to backend

reabse following::

    * 0fd32bb - (HEAD, idning/mget-improve, mget-improve) unchange (10 hours ago) <idning>
    * 705acab - clean code (10 hours ago) <idning>
    * 32e8559 - correct, but not clean. (18 hours ago) <idning>
    * fde1f12 - mget-improve almost done. (2 days ago) <idning>
    * b30fa4f - mget split to many mget and send to backend (3 days ago) <idning>
    * 7cf5625 - add frag_owner counter (4 days ago) <idning>

    * 8a4f5c0 - (origin/master, origin/HEAD, idning/master) Update README.md (12 days ago) <Manju Rajashekhar>
fix multi DEL, a bug on parse key, and remove assert on conn_sendv