Implement functions in \Phalcon\Mvc\Dispatcher class.

- Dispatcher->getPreviousControllerName();
- Dispatcher->getPreviousActionName();

Required by unit-test\DispatcherMvcTest.php on line 194 & 197

I "copied" code from cphalcon-1.3.1

Methodology:
- set variables in \Phalcon\Dispatcher->forward function
- implements getters in \Phalcon\Mvc\Dispatcher