Hm, I got the idea from [grunt-contrib-uglify](https://github.com/gruntjs/grunt-contrib-uglify/blob/master/tasks/uglify.js#L94-L102). I like the idea of consistent errors for this option, but you're right that `--stack` would likely be just as helpful. Whatever we go with should be used consistently across grunt-contrib for all functions input by the user, I think.

If we did decide to go with this I would just go with something simple, like: '*There was an error when generating the source map name*' followed by the error. But I'm undecided on it. 

Thoughts?

// cc @tkellen @vladikoff