Show LESS errors in console

For @larz0 to help debug LESS errors, e.g.

```
/Users/jasonsj/Library/Application%20Support/Brackets/extensions/user/extension/styles/override.less:322 variable @bc-border-radius is undefined 
```
Right, uncaught exception without a useful toString():

![image](https://cloud.githubusercontent.com/assets/1148713/3899037/d9668dc4-2274-11e4-95b5-9ad8522ebc76.png)