Move the hash generator inside the command hash strategy class.

This should make things a tiny bit faster (we are speaking about micro
optimizations anyway) but more  importantly it results in a better
encapsulation.

lib/Predis/Distribution/DistributionStrategyInterface.php

@@ -17,7 +17,7 @@ namespace Predis\Distribution;
  *
  * @author Daniele Alessandri <suppakilla@gmail.com>
  */
-interface DistributionStrategyInterface extends HashGeneratorInterface
+interface DistributionStrategyInterface
 {
     /**
      * Adds a node to the distributor with an optional weight.
@@ -40,4 +40,11 @@ interface DistributionStrategyInterface extends HashGeneratorInterface
      * @return mixed
      */
     public function get($key);
+
+    /**
+     * Returns the underlying hash generator instance.
+     *
+     * @return HashGeneratorInterface
+     */
+    public function getHashGenerator();
 }