Yet another username extraction fix. Thanks again @demimismo.

Closes #100 (yet again)

lib/cartodb/server_options.js

@@ -281,7 +281,7 @@ module.exports = function(){
         sql = sql.join(';');
 
         var dbName = req.params.dbname;
-        var usr    = req.headers.host.split('.')[0];
+        var usr    = this.userByReq(req);
         var key    = req.params.map_key;
 
         var cacheKey = dbName + ':' + token;