Always consume response data in order for connection to close.

First I'd like to thank you for this nice library, it's saved me quite some time in my project!

I found a small bug though, which I've addressed. Consider the following command line app built with node:

```javascript
#!/usr/bin/env node

var RobotsParser = require('robots').RobotsParser;

new RobotsParser('http://localhost/robots.txt', '', function (parser, success) {
    if (success) {
        console.log('Robots.txt parsed');
    } else {
        console.log('Failed to parse robots.txt');
    }
});
```

Assuming localhost does **not** have a /robots.txt file and thus sends a 404 header, the parser object will be set to an `allowAll` state and the specified callback method is invoked. However, if you run this from the command line you'll notice the script doesn't actually exit for a while. This is because the requests's response data is never consumed, and so the request object is still hanging around waiting to emit its 'end' event.

According to the [node.js docs](http://nodejs.org/api/http.html#http_class_http_clientrequest):

> If no 'response' handler is added, then the response will be entirely discarded. However, if you add a 'response' event handler, then you must consume the data from the response object, either by calling response.read() whenever there is a 'readable' event, or by adding a 'data' handler, or by calling the .resume() method. Until the data is consumed, the 'end' event will not fire.

This pull request calls the [`readable.resume()`](http://nodejs.org/api/stream.html#stream_readable_resume) method a few times in appropriate places so that the connection can gracefully be closed after having served its purpose.