Getting the task names associated with a particular alias

Here is some links for context:
- https://github.com/tschaub/grunt-newer/issues/59#issuecomment-60016841
- https://github.com/tschaub/grunt-newer/pull/61

Basically it is impossible to conveniently write something like this:

``` javascript
grunt.registerTask( "validate", [ "jshint", "jscs" ] );
grunt.registerTask( "default", [ "newer:validate" ] );
```

Start with the linked issue comment and pull request, then trace the grunt.registerTask entry point used by the example. Determine how callers can retrieve the task names associated with an alias, and verify that the validate/default registration scenario is supported.

Written by the indexing model from the issue text.