Show useful error messages for promotion rules and actions

Before and after images attached
![screenshot from 2013-07-11 10 16 23](https://f.cloud.github.com/assets/540762/782195/f4e0f64c-ea36-11e2-933f-df1045b5a099.png)
![screenshot from 2013-07-11 10 16 06](https://f.cloud.github.com/assets/540762/782196/f4dfbdcc-ea36-11e2-854e-08d2c0643fe5.png)