Move note about username extraction to cartodb_request

app/controllers/app.js

@@ -210,7 +210,6 @@ function handleQuery(req, res) {
     var requestedFilename = params.filename;
     var filename  = requestedFilename;
     var requestedSkipfields = params.skipfields;
-    // if the request contains the user use it, if not guess from the host
     var cdbUsername = cdbReq.userByReq(req);
     var skipfields;
     var dp        = params.dp; // decimal point digits (defaults to 6)

app/models/cartodb_request.js

@@ -8,6 +8,9 @@ function CartodbRequest() {
 
 module.exports = CartodbRequest;
 
+/**
+ * If the request contains the user use it, if not guess from the host
+ */
 CartodbRequest.prototype.userByReq = function(req) {
     if (req.params.user) {
         return req.params.user;