Grunt jshint: ensure the file passed with --file=filename.js matches all or part of the filepath before checking string lengths. Makes it possible to pass a file with full or partial path. All of these would work properly: 
admin-bar.js, wp-includes/js/admin-bar.js, src/wp-includes/js/admin-bar.js. Props atimmer, fixes #25992.

git-svn-id: https://develop.svn.wordpress.org/trunk@26168 602fd350-edb4-49c9-b593-d223f7449a82