[TASK] Set TYPO3 version to 6.0-dev

Change-Id: I4b21e237b4502f07ae1660d3e538759c716a1f4b
Reviewed-on: http://review.typo3.org/11511
Reviewed-by: TYPO3 v4 Release Team
Tested-by: TYPO3 v4 Release Team