ARM, Chapter 22: Fix anova_radon_nopred.stan, generate Figure 22.4

- `anova_radon_nopred.stan` didn't compile due to duplicate vars (`s_a`, `s_y`, and `e_y`) in the `generated quantities` block
- Generate something close to Figure 22.4 in 22.4_DoingANOVUsingMLM.R

Original Fig. 22.4
![image](https://cloud.githubusercontent.com/assets/637011/3068516/5d538afe-e28f-11e3-81cb-ffbd9bdf0467.png)

Generated figure
![image](https://cloud.githubusercontent.com/assets/637011/3068508/4ad7a824-e28f-11e3-81be-c55a787e0f67.png)