return type "undefined" listed unnecessarily

[wkeese]

This is different from #24.

I'm seeing "undefined" listed unnecessarily as a return type from dijit/a11y.js::hasDefaultTabStop(). A simpler test case is:

dijit.hasDefaultTabStop = function(/*Element*/ elem){
    return true;
};

It gets flagged as having two return types.

There's something weird going on because I can make the hasDefaultTabStop() definition work by changing the definition of isTabNavigable() (which calls hasDefaultTabStop()).