Create the Predis\Response namespace.

All of the response interface, classes and exceptions have been moved
into this namespace.

tests/Predis/Command/StringStrlenTest.php

@@ -108,7 +108,7 @@ class StringStrlenTest extends CommandTestCase
 
     /**
      * @group connected
-     * @expectedException Predis\ServerException
+     * @expectedException Predis\Response\ServerException
      * @expectedExceptionMessage Operation against a key holding the wrong kind of value
      */
     public function testThrowsExceptionOnWrongType()