Implement sockets commands for HAProxy 1.4+

[inkel]

So far the only commands that works are for HAProxy 1.3.x

Missing or not fully implemented commands:

• clear counters
• clear counters all
• disable server /
• enable server /
• get weight /
• help
• prompt
• quit
• set timeout cli
• set weight / [%]
• show errors []
• show sess

More info at http://code.google.com/p/haproxy-docs/wiki/UnixSocketCommands