add internal metric counters to gmetad server on port 8652 /status

server info and metrics collected so far...

{
  host: "vagrant-ubuntu-raring-64",
  gridname: "unspecified",
  version: "3.6.0-1",
  boottime: 1392590058909,
  uptime: 661,
  uptimeMillis: 661720,
  metrics: {
    received: {
      all: 1485
    },
    sent: {
      all: 6438,
      rrdtool: 0,
      rrdcached: 5133,
      graphite: 1305,
      memcached: 0,
      riemann: 0
    }
  }
}
Merge pull request #135 from satterly/feature/gmetad-internal-stats

add internal metric counters to gmetad server on port 8652 /status
add incby(n,v) to ganglia scoreboard for incrementing by a number

also, change the type from int to unsigned because overflow of
signed integers is undefined. This should not effect existing
metrics for ganglia agents because they are reset-on-read.

See http://stackoverflow.com/questions/18195715