TYPO3 Core

If a TYPO3 installation uses the UTF8-enabled
filesystem to allow uploading of any file name,
it is possible to upload files named myimage.JPEG
instead of automatically lower-cased etc.

A lot of checks for the file extension in the TYPO3
Core are done to check via GeneralUtility::inList()
which only checks for the lowercase file endings.

The bigger picture is to have this in a centralized
place to check if the file can be processed, but for
now, all the checks that still didn't work are replaced
by checking for a lower-cased file extension.