Method.http allow non-UTF8 encoding

when http response encoding is gbk, need convert to utf8 via [node-iconv](https://github.com/bnoordhuis/node-iconv)

```
  Meteor.methods({getMyFunds: function() {
    this.unblock();
    var result = Meteor.http.get("http://hq.sinajs.cn/list=of110002"
      , { encoding: "base64" }
      );
    if (result.statusCode === 200) {
        var require = __meteor_bootstrap__.require;
        var Iconv = require('iconv').Iconv;
        var iconv = new Iconv('GBK', 'UTF-8//TRANSLIT//IGNORE');
        return iconv.convert(new Buffer(result.content,'base64')).toString();
    }

  }});
```

[another link about this problem](http://stackoverflow.com/questions/5135450/nodejs-http-response-encoding)