Consider $foo and @foo as referring to different variables

I tried compiling mixed-vars.kit with CodeKit (1.9.3) and it failed:
![skjermbilde 2014-11-05 kl 10 07 01](https://cloud.githubusercontent.com/assets/618076/4915277/b50528d2-64cd-11e4-8a78-a07fc59b712d.png)

This PR simply considers variables created with $ and @ as referring to different variables. The expected output is compiled using CodeKit.