version 2.0.9/2.1.4 breaks some test suites

First commit just change Version check to '5.6.0-dev' (as 5.6.0 is not yet release).

With this, running phpunit for doctrine/annotations

    There was 1 error:
    1) Doctrine\Tests\Common\Annotations\PhpParserTest::testClassFileDoesNotExist
    PHPUnit_Framework_MockObject_RuntimeException: Internal classes cannot be mocked without invoking their constructor in PHP 5.6.0beta4
    /dev/shm/BUILD/annotations-a11349d39d85bef75a71bd69bd604ac4fb993f03/tests/Doctrine/Tests/Common/Annotations/PhpParserTest.php:46

Second commit use a better unserialize hack.
The regression is only for Serializable internal classes.

With this, same test suite:

    OK (370 tests, 894 assertions)

Remaining case : test suite on a class extending an internal Serializable class (ex: SplDoublyLinkedList)