jasmine: Allow done() to take an optional error.

It is a popular pattern to pass an error object to a done() callback in NodeJS. We should support that in Jasmine 2.0, too so that users can properly unit test asynchronous code.

Example

describe('async with error', function() {

  it('should fail on done(err)', function(done) {

    setTimeout(function() {
      done(new Error('async fail'));
    }, 100);
  });
});

should fail with

error: 'async fail'

instead of succeeding which is the case as of v2.0.0.