[TASK] Abstract t3lib_file_exception_abstractFileOperationException

Class t3lib_file_exception_abstractFileOperationException is never
thrown itself and only extended. It should be abstract.

Change-Id: I98611945801259cb9aa9ee24e6aa6649d327e179
Releases: 6.0
Resolves: #39817
Reviewed-on: http://review.typo3.org/13696
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn