Empty request params with XmlHTTP Post request
When I try to perform POST request with Ajax, the server hangs eating 94% to 100% of the CPU core on Ubuntu 14.10.

Here's client's script, which works (`GET` request, and if we change it to `POST`, jester hangs):

``` javascript
    jQuery.ajax({
        contentType: 'application/json',
        dataType: 'json',
        data: {
            userId: document.getElementById('user-id').value
        },
        type: 'GET',
        url: '/handle-this',

        success: function(data) {
            switch (data["result"]) {
            case -2:
                alert("malformed json");
            case -1:
                alert("Bad session id");
            case  0:
                alert("Success");
            }
        },

        error: function() {
            alert("Error saving cheat response");
        }
    });
```

and the server handler:

``` nim
echo request.params    # Prints: {:}
try:
    sessId = request.params["userId"]
    echo sessId
except:
    respJson Http200, """{"result": -1}"""
```

Everything works fine with `GET` request (parameters are parsed and passed into handler), and does not work with `POST` request, parameters are empty and the server hangs at `sessId = request.params["userId"]` line.
