fix to handle max open file limit
add curr_connections and total_connections counter and put into stats
maintain a safe number for max client connections to solve ENFILE issue
disallow zero weight in the servers section of conf
Merge branch 'safe_max_connections' of github.com:allenlz/twemproxy into allenlz-safe_max_connections
format changes
Merge branch 'allenlz-safe_max_connections'