Normalize params from URI and params has together

If you make a GET request with params both in the URI and in the params hash like:
```
HTTP.get("http://example.com?foo=bar" , :params => {:baz => 'quux'})
```
It results in a URI like this with two questions marks in it:
```
http://example.com?foo=bar?baz=quux
```
This patch attempts to normalize the params coming from the URI and from the params hash together. It produce a URL like this from the GET request above:
```
http://example.com?foo=bar&baz=quux
```