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

Add internal gmetad metrics similar to the internal gmond metrics currently available. Metrics are returned if the interactive port 8652 is polled with "/status" or "GET /status HTTP/1.0". The configure options `--enable-status` needs to be supplied to make these metrics availabe. eg. `./conifgure --with-gmetad --enable-status`

The 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
    }
  }
}
```
suggestions for other metrics to collect or changes to the above are welcome.