Handle EADDRINUSE

no ref
- Show a human readable message on EADDRINUSE

---

Prevents the all too common stacktrace below and shows a nice message instead.

```
events.js:72
        throw er; // Unhandled 'error' event
              ^
Error: listen EADDRINUSE
    at errnoException (net.js:901:11)
    at Server._listen2 (net.js:1039:14)
    at listen (net.js:1061:10)
    at net.js:1143:9
    at dns.js:72:18
    at process._tickDomainCallback (node.js:459:13)
    at process._tickFromSpinner (node.js:390:15)
npm ERR! weird error 8
npm WARN This failure might be due to the use of legacy binary "node"
npm WARN For further explanations, please read
/usr/share/doc/nodejs/README.Debian
```
It doesn't really matter whether we're handling the error or not - Ghost could not start properly and should indicate the failure to the process that started it. 

See: http://tldp.org/LDP/abs/html/exit-status.html

This is in line with tools like `ls`:

```
~% ls foobar
ls: foobar: No such file or directory
~% echo $?
1
```

It returns a non-zero status although it handled the error (failing `stat` system call).