This moves the "typo3/index.php" to the backend extension
as "backend.php". The "typo3/index.php" becomes a stub which
includes the "backend.php".

This setup works in the following cases:

1) Package "typo3/cms" is the root package
2) The "typo3/" directory is symlinked into the web-dir
3) The "typo3/" directory is copied into the web-dir

Resolves: #73026
Releases: master
Change-Id: I0e171d03cbca9e3cd91d9dc94b01f16b6109ac5d
Reviewed-on: https://review.typo3.org/46392


Reviewed-by: Joerg Boesche <typo3@joergboesche.de>
Tested-by: Joerg Boesche <typo3@joergboesche.de>
Reviewed-by: Susanne Moog <typo3@susannemoog.de>
Tested-by: Susanne Moog <typo3@susannemoog.de>
Reviewed-by: Gordon Brüggemann <gordon.brueggemann@gmx.de>
Tested-by: Gordon Brüggemann <gordon.brueggemann@gmx.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>