Assert that Session has an error message

 The seeSessionHasValues cannot be used, as Message bag Object is returned by Laravel4

  Useful for validation messages and generally messages array
   e.g.
  return Redirect::to('register')->withErrors($validator);

  Example of Usage

  $I->seeSessionErrorMessage(array('username'=>'Invalid Username'));
Merge pull request #849 from elijan/1.8

Assert that Session has an error message