Correctly parse multi-line error messages in the editor.

Before, weirdly-formatted error message:

![before, weirdly-formatted error message](https://cloud.githubusercontent.com/assets/439616/2990209/51dbcfa0-dc6e-11e3-9b38-d43db40d4709.png)

After, pretty multi-line error message:

![multi-line error message](https://cloud.githubusercontent.com/assets/439616/2990211/553b515c-dc6e-11e3-9da9-2d96998c9f51.png)