use libmongo-client in async way

hi, algernon

    I used libmongo-client in  my database middleware (mevent), which is a daemon server hold fastcgi data request.  On mongod failure or busy, web interface failed is ok for me. But when mongod reborned, I need web interface turns ok automatically. So, I set timeout on mongo_sync_reconnect(), and remove MSG_WAITALL of recv(), and redo packet_recv on h.resp_to < rid .

    This is mainly changed I made to libmongo-client, please check it.