The INSTALL_TOOL_ENABLE file is automatically created, if a backend
administrator opens the Install Tool from the backend.

Change-Id: I10ccf35f787ffdfec7becfd182b13e986258fe4a
Resolves: #28621
Reviewed-on: http://review.typo3.org/3959
Reviewed-by: Chris Zepernick
Reviewed-by: Ingo Pfennigstorf
Tested-by: Ingo Pfennigstorf
Reviewed-by: Susanne Moog
Tested-by: Susanne Moog