updates for Grunt

Apologies about the double issue. Apparently merging against master will include all other commits since then as part of the pull request. OK, let's try this again:

I made a couple of changes to your Grunt implementation that you have open as a pull request (#2344). Since there's still active debate about getting this accepted, I think keeping it as up to date and as easy to merge as possible will help keep this relevant. Here's what's been changed:

* <del>fixed merge conflicts with master</del> (but they're pretty minor, fwiw)
* updated grunt-contrib-uglify to 0.2.0
* added sourcemap support (yet another reason to switch to uglify via grunt)
* re-tabbed Gruntfile.js to match project conventions & cleaned up extra whitespace 
* edited minified banner to match what's currently in circulation

Merging this should automatically update the other pull request.