[tests] Improve the basic framework of our test suite.

We now have a base test case class for Predis (namely PredisTestCase)
grouping various commonly used utility methods shared by all of the
tests in the suite, greatly improving reusability.

NOTE: Backported from v0.9-dev.

tests/Predis/Protocol/Text/TextCommandSerializerTest.php

@@ -11,12 +11,12 @@
 
 namespace Predis\Protocol\Text;
 
-use \PHPUnit_Framework_TestCase as StandardTestCase;
+use PredisTestCase;
 
 /**
  *
  */
-class TextCommandSerializerTest extends StandardTestCase
+class TextCommandSerializerTest extends PredisTestCase
 {
     /**
      * @group disconnected