Rewrote Stringy::pad to be DRY.

Fixed "Class 'CommonTest' not found" error when running specific tests in PHPUnit by including tests directory in Composer's autoloader.

tests/StaticStringyTest.php

@@ -141,25 +141,6 @@ class StaticStringyTestCase extends CommonTest
         $this->assertEquals($expected, $result);
     }
 
-    /**
-     * @dataProvider padProvider()
-     */
-    public function testPad($expected, $str, $length, $padStr = ' ',
-                            $padType = 'right', $encoding = null)
-    {
-        $result = S::pad($str, $length, $padStr, $padType, $encoding);
-        $this->assertInternalType('string', $result);
-        $this->assertEquals($expected, $result);
-    }
-
-    /**
-     * @expectedException \InvalidArgumentException
-     */
-    public function testPadException()
-    {
-        $result = S::pad('string', 5, 'foo', 'bar');
-    }
-
     /**
      * @dataProvider padLeftProvider()
      */