Added unix socket support to node-http-proxy

Created by: buschtoens

http-proxy finally supports unix socket paths. This closes this issue. You can now do stuff like this:

var httpProxy = require("http-proxy");

var options = {
    hostnameOnly: true,
    router: {
        "mywebsite.com": "/tmp/node-http/mywebsite"
    }
};

var proxyServer = httpProxy.createServer(options).listen(80);

I mainly altered the ProxyTable.getProxyLocation function. Before it tries to split the given target string into host and port it now looks for a leading slash which determines a socketPath.

This commit is tested on normal routing like shown above. I haven't tested it on direct targets and WebSockets but it should work.