[TASK] Set TYPO3 version to 6.1.12-dev

Change-Id: I4730011c59c4a6ece14f8156a329ddfd9fce8a2d
Reviewed-on: http://review.typo3.org/32938
Reviewed-by: TYPO3 Release Team <typo3v4@typo3.org>
Tested-by: TYPO3 Release Team <typo3v4@typo3.org>