Update CakeResqueBootstrap.php to use Cake 2.x 2.x magic (a.k.a. use ShellDispatcher).

CakeResqueBootstrap.php is quite old and carries 1.3 bits.

This approach, loads and instantiates the core's ShellDispatcher (replicating the logic inside lib/Cake/Console/cake.php), without actually calling ShellDispatcher::run(), with the benefit of using the actual logic to init all constants, handlers and environments.

Also, App class magic can be later used to load other classes.