Update dependencies

 * `closure-util@0.12.0` - force inclusion of deps.js files when compiling
 * `jshint@2.5.1` - various enhancements and fixes (https://github.com/jshint/jshint/compare/2.4.4...2.5.1)
 * `walk@2.3.3` - directory exclusion fix

I added [documentation](https://github.com/openlayers/closure-util/blob/master/readme.md#publishing) on publishing new versions of the `closure-util` package.  Let me know if anybody is interested in trying it out (even for just a quick doc fix).  It will be good to have multiple maintainers.