filters and controllers can be overwritten with undefined

[tilmanschweitzer]

angular('myModule').controller('myController', function () {});
angular('myModule').controller('myController');

Second line throws no error, although the controller is overwritten with undefined. The second parameter in angular.Module.controller and angular.Module.filter is not optional and the controller/filter is overwritten.

[tilmanschweitzer]

Closed with #3