Export JSHINT if CommonJS modules are available

Export `JSHINT` if CommonJS modules are bringing in the distribution via `require` e.g.:

    jshint = require("/path/to/jshint.js").JSHINT;

[We're](http://typesafe.com/) developing a series of JS [sbt plugins](http://www.scala-sbt.org/) that will be used from the [Play web development framework](http://www.playframework.com/). Our plugin for JSHint will download the artifact via Webjars and then require it from its own JS script.