Adding Skip to mb_strrpos test case. Skips the test if mbstring is in…

…stalled and php version is 5.1.x. mb_strrpos had an incompatible function signature in these versions.

cake/tests/cases/libs/multibyte.test.php

@@ -4786,6 +4786,10 @@ function testMultibyteStrripos() {
  * @return void
  */
 	function testUsingMbStrrpos() {
+		$skip = extension_loaded('mbstring') && version_compare(PHP_VERSION, '5.2.0', '<');
+		if ($this->skipIf($skip, '%s PHP version does not support $offset parameter in mb_strrpos().')) {
+			return;
+		}
 		$string = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789';
 		$find = 'F';
 		$result = mb_strrpos($string, $find);