Use lodash mixins to supply src file paths

(this was moved over from https://github.com/gruntjs/grunt/issues/680#issuecomment-24267002, since it was off-topic)

I created this project, [resolve-dep](https://github.com/jonschlinkert/resolve-dep) to make it easy to add the resolved paths to node modules (from dependencies) to the `src` array of file paths. For example, in assemble you could `npm install` a bunch of handlebars helpers, then add the paths to the helpers to the assemble options, like this:

``` js
{
assemble: {
options: {
// _.load() mixin using resolve-dep
helpers: ['<%= _.load("helper-*") %>']
}
}
}
```

The expanded file paths to the helpers would look something like this:

``` js
["node_modules/helper-foo/lib/helper-foo.js", "node_modules/helper-bar/lib/helper-bar.js"]
```

Currently, I believe Grunt calls `toString` on the array of file paths returned by the mixin, so the example I gave above doesn't actually work (it works if you use the mixin to specify one file at a time).

I see use cases for this pretty often, any suggestions on how this can be solved?