Display compile errors in Try CoffeeScript more clearly

The error message the display for a compile error in Try CoffeeScript isn't very noticeable, and is often cut off because of the lack of room.

![](http://i.stack.imgur.com/vNSy6.png)

This change displays the compile error in red where the compiled source code would be, and dims the "Run" button to indicate that it's disabled.

![](http://i.stack.imgur.com/SrOu9.png)

You can see this [running on my `gh-pages` branch](http://jeremybanks.github.com/coffee-script/#try:alert%20%22Hello%20CoffeeScript!%22%20invalid).